I do search engine optimization as a big chunk of my job so I could type forever on this subject. In my opinion Google is still the best, but the gap isn't what it was about a year or two ago when the deficit was huge. I like the methodology behind Teoma a lot and the unheralded Wisenut has amazing potential (in fact, I'd almost wager that if its index were the same size as Google's it could easily be equal to Google, however its index is only a fraction the size of Google's.) FAST, aka alltheweb.com, also turns in decent results and I use it quite a bit since its index is supposedly larger than Google's. Yahoo just bought Inktomi so it'll be interesting to see what they do with that technology.
For the majority of searches, which tend to be very generic in nature, Google is great due to its overwhelming dependence upon link popularity thus pointing people to supposed hub sites. However, for specific searches Google really isn't that much better than any of the other search engines. The main thing it has going for it here which still makes it seem that much stronger is that its index is so gigantic in comparison to most of its rivals. Give them all the same size index and the difference on a lot of the more specific searches would nearly go away.