DH and I did a split stay in late Feb 2005, 4 nights each in Saba and Statia - we stayed at the Old Gin House and dove with Golden Rock. I posted a trip report here, if you do a search, I'm sure you'll find it.
Saba pinnacles were amazing, but we really took a shine to Statia (island and the diving). Think we're going to head back in spring 2006 for a week and skip Saba altogether, in fact.
The island itself is lovely and very quiet, old Caribbean style, not a kazillion people everywhere - I recommend a hike up to the Quill, and make sure you try out some of the restaurants in the area (get there early, as they close early), the locals and expats are friendly and wonderful. Glenn and Michelle at the hotel are fantastic, and we really liked the dive staff, too.
I concur with Warm Water Diver's choices of dives - we also enjoyed the Charlie Brown and the Chien Tong, though they are newer artifical reefs and not covered with life like wreck city! Listen up while you're there - the humpbacks were migrating during our trip in early spring, and they were so loud that it was quite disturbing!
Have a great time!