Haha, I love Heero and Zechs, but really Trieze has got to be the most amazing of all.  The man was taking down Virgo IIs as if they were nothing; seriously, compare the way he seems positively BORED fighting them with the way the Wing Boys struggle against the Virgos in the final episodes.  Not to mention that the man is kicking ass in a Tallgeese variant - screw Gundams, Tallgeese ftw.
Wish Epyon got more screentime, too.
Trieze has got STYLE, at first you think hes evil then u just cant help but feel that his not really an evil, more like hes just on the opposite side. He is as skilled in an MS as he is with a sword and thats saying sumthing, hes a better pilot than wu fei (tallgesse vs nataku upgrade) and he seemd to effortlessly duel with wu fei before allowing wu fei to kill him. I dont really know though, Heero and Zechs master the zero system, could trieze. Coz if trieze could master it, that would amplify his skills even further to a point where if u put him in epyon, you have a scarpyard of mobile dolls, lol.
Its intersting though how of all the highly acclaimed gundam pilots, Heero is the only one with skills that really shine. The other 4 are just ....there. Heero, trieze and zechs are by far the 3 most outstanding pilots in Wing but I would maybe still lean to Heero (he beat Zechs in close combat using a gundam that wasnt really suited to close combat, nice) but Trieze we will never know how good he could have been in epyon 

Epyon was the only suit which grabbed my attention in wing, unlike seed and 00 in which most suits grabbed my attention. I thought epyon got fair screentime, from when it first appeared, seemed to appear the msot, unless you mean you wish it had appeared earlier, in which case I think it was more special it appeared later in the series.
But really Gundam xx>gundam x> all (at least in the game hehe)