This ain't even a fair contest.
DIR EN GREY has been flawless since day one. They are pioneers. Luna Sea and X Japan started the scene, Diru took it and ran with it and has pioneered pretty much every advance in the genre since then, even though they've now left it behind. Case in point, there is no VK band that has not taken influence from them, and some other excellent bands (such as MERRY and 12012 and, somewhat ironically, the GazettE) basically wanted to be DIR EN GREY before coming into their own. (Okay, to clarify, 12012 CAN be awesome, but are not consistently so.)
the GazettE has always been hit-and-miss for me, but undoubtedly they are still one of the best bands in the VK scene. I was really into NIL back when that came out. I also like beautiful 5 [shit]ers from one of their first minis. And that semi-recent single, RED. Haven't really tried to listen to DIM, TOXIC, or DIVISION. Stacked Rubbish was...weird, but not rubbish.
DIR EN GREY has been consistently producing better material every album, but their old stuff is still great. Okay, except maybe Vulgar -> Withering. I still like Vulgar better. But Dum Spiro Spero is perhaps my favorite album ever from any artist in any genre. I know they got a lot of hate for it, but I love it.
So yeah, DIR EN GREY.
I don't think GazettE was a good match up, but I can't really think of another band with similar skill AND popularity to DIR EN GREY. They are plenty of bands that are as skilled or more so but nowhere near as popular, so its tough. Maximum the Hormone could definitely give them a run for sheer craziness and ferocity, but they're not on the same level commercially. Plus, Kyo and Daisuke both had throat surgery due to their crazy vocal antics.