MT with bits from T4 and T20. I steal T4 psionics, and T20 T&C. I'm also using T20 ship design in current campaign, but players neither know nor care.
I have core rules for all but GTIW. I have some stuff for each edition.
rules:
CT Bk0-8 (1-3 & 5 are second ed)
CT Supps 1-13
CT SS3
CT Adv 1-12
CT DblAdv Reprint.
CT TTB, TTA, AM1-8, BoJTAS1-4, SMC, Beltstrike
Old Games: Imperium, Invasion Earth, Imperium 3rd Millenium, AHL, Striker
MT PM, RM, IE, RC, RebSB, HT, AV, S&A, V&V, WBH, Knightfall, 101V, The Flaming Eye, Survival Margin
TNE Core, FF&S, BL, H&I, WTH, Striker II, RCVG, RCEG, RegSB, BL, BR
T4: Core, Pocket Empires, Psionics, Alien Archive, Squadrons, FF&S2, NAH.
T20: 2xCore, 3 items sent by Hunter (don't recall, but I think arsenal is one of them).
GT: core 3rd Ed, GTFT
T5: playtest Drafts.