Back to the topic at hand... okay let's do a detailed comparison. It's surely too simplistic to just throw numbers without context, so draws will be examined, noting quality of wins (beating good players) and quality of losses (losing a competitive match to a great player > losing a competitive match to a good player > getting dominated).
Nalbandian has: 1 F, 4 SF, 5 QF, 4 4R.
Final (WB): really mug draw, not a single top 20 seed faced. Played five sets vs Lapentti and Malisse, then got crushed by Hewitt. So no particular great level prior to the final and a no-show in the final. One of the weakest slam final runs in the OE (barring demoted AOs, of course), little better than Anderson's much-maligned USO 2017 run.
Semis (1 AO, 2 RG, 1 USO):
2006 AO: looked pretty good throughout (though the draw was easy), but ended up imploding badly against unheralded Baghdatis in SF - not only from two sets up, but also from 4-2 up in the final set, and that was a bad choke. Second worst way to lose imo (worst being a rout).
2004 RG: looked great before SF, but again an implosion. Gaudio was playing quite well, so it ended in straight sets. Nalbandian was *5-2 up in the second set (double break lead), lost in TB then got bagelled.
2006 RG: goated for a set and a half vs Fedr (up 6-3 3-0), lost the plot (again!), eventually got overwhelmed by stomach cramps and retired down a double break in the third set.
2003 USO: best career run - beat solid Federer and Aynaoui and almost outclutched peak Roddick in straight sets... right until the match point. MP lost, tiebreak lost, next two sets lost 6-1 6-3 without much fight.
Quarters (3 AO, 1 WIM, 1 USO):
2003 AO: good win over young Fedr, then... WTH was that? 6-1 6-0'd by Rainer Schüttler? Terrible loss.
2004 AO: reached QF in straights and lost a competitive four-setter to peak Fed, strong run.
2005 AO: lost 10-8 in the fifth to peak Hewitt. An up and down match, but still a great effort, worth being called a strong run.
2005 USO: lost easily to Federer, nothing special.
2005 WIM: nice win over young Gasquet, but lost easily to Johansson after the first set.
Fourth rounds (1 AO, 2 RG, 1 WIM):
decent losses ay WIM 03 and RG 07 - close four-setters vs Henman and Davydenko respectively. 6-1 6-2'd by Hanescu at RG 05 - no good, fairly easy loss to Haas after taking the first set - no good either.
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Davydenko has: 4 SF, 6 QF, 4 4R.
Semis (2 RG, 2 USO):
2005 RG: nice wins over Coria and Robredo, lost in five to Dopuerta also wasting 4-2 (in the fourth set). Dopuerta was better than Baghs though.
2007 RG: beat Bandy en route, lost a very close straight-setter to Federer; Denko was close to winning each set but couldn't make it, serious set-level choking but still running peak Fed close is alright.
2006 USO: beat Haas in QF, lost SF to Fred in straights, not that close though Fed didn't entirely cruise.
2007 USO: beat Haas again and lost to Fed in straights again, that was close for two sets though rather messy.
Quarters (4 AO, 2 RG):
2005 AO & 2009 RG: lost in easy straights (Roddick, Söderling).
2006 AO: a very close four-setter against a subpar but still peak age Federer. Choke moment at the end of the third, strong stuff otherwise.
2006 RG: so-so four-set loss to Nalbandian.
2007 AO: lost 7-5 in the fifth to Haas.
2010 AO: led Federer up a set, a break and BP for a double break, then imploded to lose 11 straight games. Recovered to make the fourth set competitive though.
Fourth rounds:
Nothing special. First two sets of 2009 USO vs Söderling were good but Davydenko got hurt in the third and retired.
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Conclusion:
Nalbandian clearly had a higher peak (as I mentioned before), but kept running out of gas or succumbing to nerves at the end of his best runs, starting strong but eventually melting down. Out of his QF+ runs, the only two losses where that didn't happen were 2004 & 2005 AO; those two Nalbandian finished as well as he started, Federer/Hewitt was just better all in all.
Davydenko happened to run into Federer in 3 of his 4 SF losses so that skews the picture. He lost all those in straight sets, but 6 of the 9 sets were 7-5 or 7-6 - close but no cigar. I'd say it's better than Nalby's RG semis though, and the lolbledon final run. Nalbandian's USO 03 does stand out as the best slam campaign for either player, the closest they got to winning a slam (just one more point, and Ferrero in the final), but the total meltdown once Roddick snatched the set detracts from it. Davydenko's quarters were clearly better (4 good vs 2 good). Nalbandian's fourth rounds were better. Seems close as it is, slight edge to Bandy at most but imo better called even.