I have many favorites, but I feel special attention needs to be paid to this one:
Sandrock Custom.
The redheaded stepchild of Gundam Wing. The one everyone forgets about, the one most people outright dislike.
I love the earthy colors and the stout build, the giant solid blades with both a graceful and meacing look, the Roman headpiece and the snakehead shield. It's solid as a rock and unmovable as a mountain.
Add in the new armor cape from GoL and the cloth cloak (which the rest of the Wing Gundams have adopted as well in FT) and it's quite a beautiful machine to behold. Such a shame it's not featured in more games or merchandise.