Peak level of play goes to Safin, he's clearly a more skilled tennis player than Roddick (and yes, he put the work in to fully heal up after 2003, but that has no bearing on the discussion of how their games matched up on Rebound Ace). But at a certain point, it has to be asked; what did you do with those skills when you weren't hurt?
He got some awesome clay court scalps, sure. Did he capitalize and win consistently once he smoked the big names?
His talent was trumpeted from the moment he got on tour. Did he try to maximize it when he was fully healthy?
He was better on carpet and clay and (slow, Roddick takes fast) HC. Wonderful. Why then did it seem like a crapshoot as to whether or not he would beat himself when he was 100% even on those surfaces, whereas you always knew that Roddick would go out and work his ass off, even if he wasn't favored?
In a vacuum, skill should decide everything. Safin had - and probably still has, to be honest - a lot more skill than Roddick, and yet has a very similar career barring the one additional major (which again, is quite large) and DC (large depending on who you talk to) when really, he should have had far, far more, even taking his injuries and the eventual rise of the Big Four into account. There's a reason tennis matches are contested on court and not paper; Safin could and did look like a worldbeater on some days, but he had so many off days for whatever reason that it hurt him greatly in evaluating his overall career, which should be measured in more than just highs. Roddick did almost as well with significantly less in his arsenal; like you enjoy pointing out, there's no doubting who the more skilled tennis player was, and it's because of the skill gap and the lack of achievements that came in spite of it that make me unable to give Safin the full nod.