The 4030 should have the best picture assuming you have a light controlled room as it has the best contrast but buying used is always a gamble. If you can set it up and verify it has no burned polarizers or dust blobs it's the best deal. If you want a warranty the 3100 is the best deal if you need lens shift and the added brightness for a less then ideal room. The 2150 is decent if you don't need the lens shift or brightness of the 3100.
"Smart enough to know better, to old to care" ------ Dedicated Bat Cave Home Theater, JVC RS49U/Mitsubishi HC7900DW Projector, 110" 16:9 Jamestown screen with variable power masking for CIW 2.50:1 to 16:9, Marantz 7009 with 7.1.4 Atmos with Ohm mains,3 DIY Subs (2 15" (1 ported, 1 sealed and a 12" 4th order bandpass), 1 DIY butt kicker, Custom Built HTPC, 18TB DroboFS NAS