Bill:
I've never been to either but am interested in both. I'm told Saba entails pinnacle diving; underwater mountain tops extending up into recreational depths (but can still make for deep dives), if I understand correctly, and it's pretty much all boat diving.
If I were you, I think I'd spell out what kind of diving I like to do. Do you like long, shallow to deep coral reef like swimming along Bonaire's west coast sites? Do you enjoy drift diving in Cozumel and like to see larger animals? Is there some animal, such as a shark, you're eager to see? Do you especially like low current waters? Would Saba and Statia diving tend to differ on average depth of sites chosen? I ask because an air hog might like shallower diving, if one or both didn't have ready access to larger-than-80 cf tanks.
Perhaps those familiar with Saba, or especially both, can comment with that in mind.
Richard.
P.S.: Haven't I read somewhere that the plan landing on Saba can be a little 'exciting?' If so, do you enjoy excitement? I hope my recall of reading about it in the past isn't wrong; if so, somebody can call me on it.