What is the Sahih Aqeedah (sound beliefs) according to Prophet (sws)? And which school of thought is nearer or exactly according to that?
The Prophet (sws) was himself guided by the Qur'an and was instructed to warn and guide by the Qur'an. The correct belief therefore is one that is based on the Qur'an.
This might seem as a too obvious and simple response, but actually it is not. Many think and claim that their belief is according to the Qur'an while it is not.
If a person wants to base his belief on the Qur'an, before learning from the Qur'an he needs to:
- throw away any assumptions
- get rid of any sectarian prejudice
- consider the Qur'an as the ultimate reference for truth (e.g. accepting its verdict even if it is against the general belief of a big number of Muslims)
- consider the Qur'an as the independent reference for truth (e.g. not attempting to understand the Qur'an based on any external sources - other than the knowledge of the language of course)
- consider the Qur'an as the container of all the beliefs that a Muslim needs to hold to succeed in the hereafter (e.g. not to hold any belief taken from outside of the Qur'an as an essential part of belief)
As for what school of thought is nearer, you need to examine which of the available schools of thought are closer to the above premises.
Please also note that I answered your question considering that you only asked about Aqeeda (belief), if you had asked about Aqida wa Amal (belief and practices) I would have then included the importance of referring to the Sunnah of the Prophet (sws) in my answer as well.