The ReptiSun 10.0 or the Arcadia Euro Range T8 is probably the way to go if you're using a T8 fixture. Generally, the UVB bulbs go along the lines of you get what you pay for, and the more expensive ones tend to be very much worthwhile. The higher cost of some of them (I'm thinking of the Arcadia 12% T5 in particular) can be offset by their longevity - in some cases lasting several years before needing replacement.