I like the Hulk - it is a good ride but not really scary but you do get a good rush. Not ridden Kraken so can't comment (must make a note to try it in April though).
I think Dr Doom is rubbish though - not scarey in the least.
Tower of Terror still gives me a good buzz when I ride it and I like RnR too but again don't think its scarey.
Duelling Dragons is probably the scariest - if you sit in the front and can see the other coaster approaching.
I prefer Montu and Kumba to Hulk - don't think either is scarey but they are excellent rides.
In some ways Gwazi is scarier - I'm always scared I'll come off with a back injury with all that shaking about.
I love coasters - haven't found anything that scares me yet. BUT water rides now that is a whole different matter. No way would you get me on Summit Plummit - just thinking about it makes me all shaky. I've done Kowabunga a few times and that's ok but not really my idea of fun - you will find me floating in a tube on the lazy river!!