Probably Dark Tranquillity, due to their fairly unique sound and high level of consistency...while they had some dodgy moments on Projector, the rest of their discography is fairly solid, sometimes to the point that people think they sound too homogenous (but, in reality, their sound does vary from album to album). They've also been far more than just another 'let's recycle some Maiden riffs' Gothenburg band to me (although some people may disagree[sup]1[/sup]...)
However, after DT (and they only just rise above my third favourite bands), there's a huge mass of bands that come to the forefront regularly (Megadeth, Priest, Slayer, Ensiferum, Tristania, Wintersun, Sabbat (at the minute) et al). I guess Maiden and DT just click with me more, as there's only one DT song I truly hate, and I love most of the rest...and I can't really think of any Maiden songs that I really despise (hell, even The Apparition has cool lyrics going for it!)
[sup]1[/sup]*coughUltraBoriscough*