which is the best book for neet UG preparation

NCERT Textbooks of Class 11 and 12 are the most important books for better understanding and problem solving. You always start your preparation with NCERTs as these are written in simple Language which is easily understandable to everyone. Once you complete your syllabus from NCERTs, you should move on to some standard refernce books for in depth knowledge in theory and solving complex numerical problems.
To do the best, you need the best books for preparation-

PHYSICS

Concepts of physics by HC Verma
Problems in General Physics by I.E Irodov
Objective questions on physics by DC Pandey

Mathematics

Truman's Biology Vol1 and Vol2
Objective Biology by Dinesh
Pradeep Guide on Biology

CHEMISTRY

Physical Chemistry by OP Tondon
Numerical Chemistry by P.Bahadur
Organic chemistry by OP Tondon

Along with this solve previous year exam papers and give mock tests as many as you can. The more you'll practice the more you can score. To help you with your Neet Preparation, go through the link http://learn.careers360.com/knockout-neet-may/