These MINI Buyers Guides are a good starting point:
Buying guide : MINI 2001-2007 - AROnline MotoringFile MINI R50/R53 Buyers Guide
I would suggest the post mid-2004 facelift R50 MINI with the stronger Getrag gearbox. MINI One for lower insurance or Cooper if you can afford the insurance for a sportier performance but both are fun to drive.