Which Dell Optiplex desktop?

I am going to be ordering some replacement desktops for one of our offices. I would like to have NT 4 WS installed and am looking at the Dell Optiplex series. This office runs an older DOS(at the client)/Pervasive SQL(at the NT 4 server) applicationon the network which handles purchase orders and and payroll. Also installed are Office 2000, NAVCE, and a dialup service using a terminal emulator and DUN. I know that the DOS application will run under NT 4. I have already tested it. Any good or bad experiences with the various Optiplex destops/chipsets?