The original question is too broad!
Both Ohmboyz and Spectral Delay kick arse and can easily produce some awesome delays.
But... (and this is where your question falls over...) it all depends on what kind of sonic result you are after. The delays mentioned can have very different results, and you'd probably want to use both (but in different situations).

Personally, I'm a fan of Ohmboyz, but if you don't need the fancy features it offers try a lower power delay to save your CPU Check out www.databaseaudio.co.uk for some free delays to try. And search around for the PSP 42 or 84 which can both do some nice stuff.

In summary - have a few delays at your disposal and use each one as appropriate!