I've only been on a Vekoma, just to let you know.
Anyway, the Vekoma one I've been on would be Rock n' Roller Coaster at MGM Studios, and I recall it being very good. Can't remember much about it since it was 6 years ago, but the whole overall experience with the theming and everything was incredible. That's about as far as my memory goes, but I know I was quite fond of it.
The Premiers don't look bad, especially not the Flight of Fear coasters, but I just think that the Vekoma ones, especially Rock n' Roller coaster, look a bit better. Though, the plusses to the Premier ones would be the lap bars and the extra turns and stuff in the layout.