Which is the best? On ebay there seems to be one that is 693.5 and one like 6012 that are very similar in price, but not in performance from what I understand

I got my 4x6 infinity plates in and haven't had a chance in install (yet)

The 692.5 speakers are from Infinity's Kappa series. They're the better quality of the two. Not sure what the 6012's are, but the 6002's are round 6.5" speakers from their Reference series, the cheaper of the two. The 9602 and 9603 are the 6x9 Reference speakers. Go with the Kappas if you have the money.