which state is better for B.Tech either Tamil Nadu (or) Andhra Pradesh
State has nothing to do with any course. It is the college that matters not the State in which the College is present until and unless you are going to study politics and all.
After all you are going to study science related stuffs so just don't think much and go for it. Yes, In Tamil Nadu you can find top colleges like IIT Madras, NIT Trichy, Anna University, SRM University, VIT University and all which in compare to the colleges in Andhra are relatively good.
All the best!!