Paal/phaal is the hottest of all but you have to ask for it specially, its never on the menu. I have had two, each time as an act of bravado. (The second time I was ringmaster for my brothers stag night and so naturally insisted we had some paals. The grinning waiters came back five minutes after serving it and asked if I was enjoying it. "Its what I expected" was the best I could manage to croak...)

My eyes are watering just remembering it.

To enjoy I don't really like anything hotter than a madras or a jalfrezi, although some restaurants are light on spices and then I might upgrade to a vindaloo.