My info is a little dated (pre-2000), but the CONUS C-21 units all seemed to be about the same as far as hours, upgrades, etc. The USAFE guys took a little longer to upgrade (at one point I think Stuttgart didn't have any initial IPs, only MWS guys).
Point is, if there's a C-21 out there, TAKE IT. It's the easiest flying job ever invented, you fly a ton, you upgrade quickly, you get to go all over the country (world sometimes) and stay in nice places, you might deploy once, you get a type rating, the sim is in Dallas, the plane's a little rocket... once I got to 130's I realized that I'd already learned how to be a nav, engineer, load, and radio operator in the Lear.
I know there's uncertainty in follow-ons, maybe some of the newer guys have more insight into that. But man, what a great gig!