Since the actual exam is written from the Schweser material, definitely use Schweser.
To each his own, but my experience was Schweser at l3 (fail) followed by CFAI material for l3 (pass - easily). However, my prior fail was close. Put in the time/effort and you can pass with either. However, if you need to own the exam in order to pass (i.e. have severe test anxiety), I’d recommend CFAI.
My $.02.