I don't mind the short spined ones. I have a green urchin that just mows down algae like nuts. I'll have to try to get a pic of it. I supposedly have a blue tuxedo but I haven't seen it in ages. I had one before that was awesome at the red fuzzy beard/stubble type algae. I also have one of the rock boring ones but it just sits in its cave mostly and occasionally ventures out but not too far. I hear it could be a scavenger as well as a herbivore.
Anyhow, they're all pretty neat. Be wary that some of them (the colourful ones) are said to have toxic stings, so do you reading. Best practise is to avoid getting stung if you can anyhow.
Here's a diadema (I just posted these pics in another thread but what the hey)..
