The only number in favor Federer is 1 more final, and that is clearly no dealbreaker, especialy as ****s have established ignoring that Sampras has 2 more U.S Open finals than Sampras, and far more longevity of success at the event, and declaring Federer light years superior despite that. Any other stats that would favor him are things involving his numerous wins at Halle, a freaking 250 event, which is beyond laughable so I wont even entertain. Beyond that both have 7 Wimbledons, Sampras actually played and won Queens (the only semi relevant grass event outside Wimbledon), while Federer never won and rarely attempted, so wont bother giving either an edge there (although if I were a **** I would surely be pumping that up, lol)
I go with Sampras because:
1. With 3 Wimbledons in a row, a 1 year defeat, then 4 Wimbledons in a row, I consider him to have dominated on grass for an 8 year span. A single year defeat in the midst of two long winning streaks is not enough to declare a break of dominance, so roughly an 8 year period of dominance. By contrast Federer did win 5 Wimbledons in a row, but after that while he did win 2 more spaced over 5 years he never won back to back Wimbledons, so his period of dominance was only a 5 year one really.
2. Sampras's grass competition was far stronger IMO. I can see the ****s already going ballistic hearing this again but lets face it considering the stats are virtually identical in every relevant sense lets face it, it pretty much comes down to personal opinion. To clarify though yes Samrpas's grass competition by 2000. However atleast for the first part of his reign there from 1993-1995 it was extremely strong, something it never was at any point for Federer.
3. I have seen both play and Sampras at his peak or in his prime played tennis at a higher level on grass than Federer ever did. In one Wimbledon final Sampras hit 68 winners and 7 unforced errors. Federer has never matched that kind of level, his best was probably 60 winners and something around 12 unforced errors vs Roddick in the 2003 Wimbledon semis, and Roddick has proven to be one of the easiest players to post clean and great stats against (although still not that easy to beat due to all his service winners mostly). Sampras had the much better serve, better volleys, better transition to net and overall net game, was overall more explosive, basically all the things that are most important on grass.