I've only had two: JHS Panther cub, and the SD Vapor Trail. Both have pots to change the modulation. I sold the JHS, namely because it costs a lot for the same important features as the vapor trail (to me). The Cub was cool for different subdivisions, and for tap tempo as well, but I just didn't need those. I also found the JHS to have a lot of range on the modulation, to the point where it was too much.
I really like the Maxon AD9Pro. Transparent when it's off and doesn't color the sound when it's on. Nice warm repeats without being muddy or gritty and a usable amount of delay for my needs.