Pretty much this.
I'm not hung up on Slam Finals as much as others might be but winning WTF is a good starting point.
Nalbandian & Davydenko pop up there but Nalbandian hands down is ahead. Mecir won the WCT when it was around plus made 2 Slam Finals and won 3 Masters.
Of course because of the Federer factor, I put Nalbandian at #1. Here's what you have to ask when talking about greatest Slam-less players, what was their opportunity? Flat out, I mean you can easily point to Roddick and say multiple Wimbledon champ if Federer ain't there and he had a hairline opportunity in 2009. Where do Nalbandian's opportunity's come in to play?
2003 US Open: Golden opportunity, golden choke. He was up 2-0 and match point in the 3rd and regardless of the fan yelling at 7-7 in the tiebreak there's no excuses losing such a match. Would have beat Juan.
2006 Australian: Another choke, up 2-0 against Baghdatis. Do I think he beats Federer in the Final? Yes I do, but we'll call it a toss-up.
2005 Australian: Forgotten epic match, Nalby down 0-2 comes back and loses 8-10 to Hewitt. Toss-up against Safin but he would have beaten Roddick to get to another Final.
2004 Australian: If this sounds like a broken record, keep in mind he was freshest for this Slam given his injury history. Still had mental edge on Roger, beat him, win it all.
2002 Wimbledon: Let's be clear, Nalbandian allowed two consecutive 2-0 leads drag into a 5th set before that final. That speaks more about him than his opponents so he doesn't win this against Hewitt or Henman.
2007 US Open: Laugh if you will but understand Nalby was up 2-1 against Ferrer and lost in a close tiebreak and then 5-7. Ferrer goes on to beat Nadal then folds against Novak in semifinal. It's not exactly insane.
So despite injuries, which really kept him back from winning at least 1, he still had 4 legitimate opportunities. One of those being a complete chokejob by him in 03, then the back to back Aussie Opens where it's 50/50.