The 5.0 GT perferably the BOSS. the 5.0 has more power stock and a blower can be added for more power. If the BOSS is an option I would go that route due to even more power than the normal 5.0 plus it has a fordged bottom end, less builing needed later boosted applications. I don't think any of the late model mustangs are going to become collector cars like the '60s did.
Forged bottom end, Ported heads, Saleen super charger, 2.8 blower pulley/15psi, Dual stage water to air intercooler, AFCO heat exchanger, battery relocated, Twin GT500 fuel pumps, T-56 trans, Aluminum flywheel, Aluminum driveshaft, 3.73 rear gears, Eaton TruTrac Diff, TA Performance rear end girdle, Racecraft suspension system, UCA, LCA, panhard bar, 15" slotted front rotors w/ 6 piston calipers, Carbon Fiber front splitter/rear diffuser, and bunch of other stuff
I would probably take a terminator if it was near new and unmolested, but since I most likely wont find one of those.. ill settle for a 5.0
05 gt auto, K&N CAI(off at the time/no tune yet), Mac LTs/prochamber/Mac ABs, Tokico adjustable shocks/struts, FRPP K springs, J&M camber plates, J&M adjustable UCA, CHE adjustable panhard bar, Roush bumper, Roush hood scoop, black out grille, gt500 wing, 315/35/20 NTO5 rear and 255/35/20 555s front on MRR wheels.