The eternal holy scriptures describe three ways of emancipation-from-Maya or God realization.

लक्षन्तुचतुरो वेदा लक्षमेकं तुभारतम्॥lakṣantu caturo vedā lakṣamekaṃ tu bhāratam॥ ​Ved Vyas divided the Vedas (also known as vinirgat granth) into 4 books and all together they encompass 100,000 hymns [1]. Of all the mantras in the Vedas,
• 80,000 mantras explicate the philosophy of karma (vedic rituals),
• 16,000 mantras explicate the philosophy of gyan (knowledge) and
• 4,000 mantras expound bhakti (devotion).

​The Bhagwat also asserts the same three paths – ​​

योगास्त्रयो मया प्रोक्ता नृणांश्रेयो वववित्सया ।
​ज्ञानंकममच भक्तक्तश्च, नोपायोऽन्योऽक्ति कु त्रवचत्॥
भा ११.२०.६yogāstrayo mayā proktā nṛṇāṃ śreyo vidhitsayā ।
​jñānaṃ karma ca bhaktiśca, nopāyo'nyo'sti kutracit॥
bhā 11.20.6

मागामस्त्र्यो मेववख्याता, मोक्षप्राप्तौ नगाविप ।
​कममयोगो ज्ञानयोगो भक्तक्तयोगश्च सत्तम ॥
दैवी भाग. पुmārgāstryo me vikhyātā, mokṣaprāptau nagādhipa ।
​karmayogo jñānayogo bhaktiyogaśca sattama ॥
daivī bhāga. pu The Ramcharit Manas and the Gita also describe these three paths of God realization. But the fifth original Jagadguru, who was honored with the title of Jagadguruttam i.e. supreme-most amongst all Jagadgurus, Shri Kripalu Ji Maharaj has conclusively proven, using references from the same scriptures, that bhakti is the one and only path to God realization. The other paths such as karma, gyan etc. can also be practiced along-with bhakti, but without bhakti, no-one has or can ever attain God realization.

At the end of Dwapar Yuga, the great saint, Ved Vyas wrote most of the scriptures – Gita, 4 Vedas, 17 Puranas, Ramayan and Mahabharat, 6 Darshan Shastra etc. But he did not experience any peace of mind. Noticing his discontent, Saint Narad suggested that He had written a lot about karma, gyan and bhakti; however, his explanations of bhakti were inter-mixed with karma or gyan. Saint Narad asked Him to compose something describing the meaning and greatness of pure bhakti. He told Ved Vyas that, that was the only way for Him to attain peace”.

Ved Vyas Maharaj heeded to the advise of Sage Narad. However, to compose a scripture on pure bhakti, practicing and personally experiencing that bhakti was very important. So, Ved Vyas performed unalloyed devotion to Shri Krishna and attained His darshan (divine vision), after which he composed the Shrimad Bhagavat Mahapuran. He revealed the esoteric facts of pure devotion along with the methods of attaining the highest achievements of life thereafter.

There are many methods of sadhana bhakti, but navadha bhakti (nine methods) propounded by Saint Prahlad, crest jewel of devotees, is the most accepted and advocated by most of the saints. It is so because navadha-bhakti encompasses most of the other methods proposed by other numerous acharyas. Navadha bhakti comprises the following -

श्रवणं कीतमनं विष्णोः स्मरणं पादसेवनम्। अचमनं वन्दनं दास्यं सख्यमात्मवनवेदनम्॥ 
भा ७.५.२३śravaṇaṃ kīrtanaṃ viṣṇoḥ smaraṇaṃ pādasevanam । arcanaṃ vandanaṃ dāsyaṃ sakhyamātmanivedanam ॥Let us understand in brief each of these forms of devotion and who performs this form of devotion.

summarize the navadha bhakti section and then conclude it

Navadha Bhakti

1. Shravanam (श्रवणं) - Listening to the names, forms, pastimes, attributes and abodes of ishtadev* is termed as shravanam. Parikshit practiced this form of devotion. He realized God by listening to the leelas of Shri Krishna written in Shrimad Bhagavat and recited by Shukdev Paramhans. ​

2. Keertanam (कीर्तनं)- chanting the names of God with feelings of love and devotion is termed as keertanam. Saint Narad practices this form of devotion to stay immersed in the divine bliss

3. Smarnam (स्मरणं) - continuous remembrance of God is termed as smaranam. Saint Prahlad followed this form of devotion and remembered God at all times even in the face of adversity.

4. Paad-sewanam (पादसेवनम्) - paad means feet and seva means to serve. Dedicatedly serving the lotus feet of ishtdev* is termed as paad-sewanam. Goddess Mahalaxmi propounds this form of devotion.

5. Poojanam (अर्चनम् / पूजनम्) - Ritualistic worship (वववि पूवमक) of one’s ishtdev is called poojan. King Prithu is the greatest example of worshipping God with this method of devotion. 

6. Vandanam (वन्दनं) - pleasing God by glorifying His names, form, pastimes, attributes and abodes is named as vandanam. Akroor adopted this method

7. Dasyam (दास्यं) - loyally serving Him with great love and dedication is known as dasyam. Hanuman Ji is an excellent example of this method of devotion.

8. Sakhyam (सख्यं)- loving God as the dearest friend is termed as sakhyam. Arjun is an example of this method of devotion

9. Atma-nivedanam (आत्मनिवेदनम्) – surrendering everything including oneself at the lotus-feet of the Lord is termed as atma-nivedanam. King Bali is the greatest example, who gladly surrendered everything including himself at the lotus feet of Lord Vaman.In Bhagavat, Shaunak and other rishis asked Paramhans Soot

यच्छ्रोतव्यमथो जप्यं यत्कतमव्यं नृभिः प्रभो । स्मतमव्यं भजनीयं वा, ब्रूहि यद्वा विपर्ययम्॥ 
भा १.१९.३८acchrotavyamatho japyaṃ yatkartavyaṃ nṛbhiḥ prabho । smartavyaṃ bhajanīyaṃ vā, brūhi yadvā viparyayam ॥
bhā 1.19.38

“For human beings what is worth hearing, chanting and remembering to attain the ultimate goal of life?”​

​This question indicates that they consider only three methods for the ultimate upliftment of mankind, i.e. shravan (hearing), keertan (chanting) and smaran (remembrance). Since

1. Shravanam - One needs to listen about the beauty, attributes, merciful nature and pastimes of God to be continuously reminded that God alone is mine and God is my ultimate refuge.

2. Keertanam - Understanding the above then singing and conveying the same message to others to fortify the knowledge and devotion.

3. Smarnam - Thus, constant reflection on God would provide the necessary impetus to meet Him. ​According to Shaunak and other sages these three are essential processes of bhakti.

​Jagadguruttam Shri Kripalu Ji Maharaj has laid the entire emphasis on smaranam bhakti (continuous remembrance of God). According to him, however large the effort might be, unless it is accompanied with smaran, it will not (rather it cannot) yield the desired result. Just like multiplying a number, however large it might be, by zero never yields nothing but a zero; without smaran performance of any of the other eight methods yields no divine fruit [2].

This is so because God records only the thoughts in His divine annals and not the physical actions. Except smaran all other forms of bhakti, stated above, are done by either action-oriented-senses (कर्मेन्द्रियाँ) or knowledge-oriented-senses (ज्ञानेन्द्रियाँ). Only smaran is done by mind (मन). Take for example – while listening to Bhagavad Katha (stories of Lord written in scriptures), if your mind is engaged in material thoughts, what will be the outcome? Will it result in peace / happiness or immerse you deeper in the material world? It will lead you deeper into the material world for sure! And that is what has been happening since eternity. Each soul has recited God’s names countless times [3], spent countless hours in pooja, yet, since the mind was not engaged in the loving remembrance of God, we are still roaming around in this world looking for the ultimate bliss.

​There are only 2 eternal realms - material and divine. If the mind is not engaged in God then it is certainly engaged in some material matters and vice-versa. “Thinking about God” means choosing one of His countless all-attractive divine forms as your ishtdev* and focusing the mind on that form. For this kind of remembrance Shri Kripalu Ji Maharaj has coined the term roopdhyan. Roop means form and dhyan means meditation. 

भक्ति मन से हो नित्य गोविंद राधे। भाव निष्काम अनन्य बना दे॥
कृपालु त्रयोदशीbhakti mana se ho nitya goviṃda rādhe । bhāva niṣkāma ananya banā de ॥
kṛpālu trayodaśī

“Mind has to be engaged in continuous devotion to God. That devotion needs to be selfless and exclusive to your ishtdev* ”. Again, he says - 

सब साधन जनु देह सम, रूपध्यान जनु प्रान। खात गीध अरु स्वान सब, कामदिक शव मान ॥
भक्ति शतक
saba sādhana deha sama, rūpadhyāna janu prāna। khāta gīdha aru svāna saba, kāmadika śava māna ॥
bhakti śataka

“All other means (such as gyan, karm, yog, austerity and rituals etc.) are like a body and roopdhyan is like the soul of devotional practice. Without remembrance all other efforts are like a corpse - a body without a soul”. 

So, according to Shri Kripalu Ji Maharaj, you may adopt any method you like but never forget to do roopdhyan - devotional remembrance.