I am doing my MS in pure mathematics and I am aspiring to become a mathematical physics. I have some familiarity with functional analysis due to some courses that mentioned some of the major theorems and also by some reading here and there, but I never really focused on the subject on its own. I've noticed how important functional analysis is for mathematical physics and so I would like to learn it in detail on my own.

The two books I am thinking of using is Lax and Reed/Simon Vol I. The latter seems to be exactly what I want since it focuses on mathematical physics, but a few friends of mine have told me that Lax is an easier read with better exposition (and easier to understand proofs), covers more, and is more modern. What do you all think of these two books? Can anyone vouch for one book over another?