I mostly use basic mounts (horse, saber, raptor, lion, raven lord, armored gryphon/wyvern) because I like them the best. The new Flamesaber mount is nice too, but it's just a reskinned saber model, so I guess it kinda falls into the list above (just more flashy).

I've never been a big fan of giant mounts that take up your entire screen or the ones that make a ton of noise, but I am a bit partial to some of the Proto-Drakes from Wrath.