Both are generally mild curries with the spiciness really only adding flavour. I prefer my butter curry to be made a little spicier as I enjoy the warmth. A green curry, particularly as I had it with coconut rice, is a very sweet affair (mostly the coconut rice does that). I am not truly sure how to further analyse why I like them, but am loathe to say "I just do."
Suffice it to say that I enjoy the blend of flavours and it is probably the best veggie intake I've had in a while. Mostly I get tomato and lettuce in small quantities, and very little else vegetable-wise. I realise I should have more fruit and veg, but sometimes that is hard to do, when I barely even think of it. Anyway, I've gotten off track (like I would ever do that!) so now I shall stop this glorious ramble!