To answer the question literally, the P4. Its got a 1.2GHz advantage Of course for all intents and purposes, i'd proly reccomend the 3500. Of course, if you step up to the Pentium4-550 then my reccomendation might swing the other way
(pause)
Wait a sec. That is the 550 (ugh c'mon people, Intel's stopped using "Ghz" as a rating). In that case, I'd give the 550 a serious lookover ... pair it up with the ASUS 925 board and you've got an unlocked setup (other manufacturers might have overcome that lock but im not sure, only heard of ASUS)