That's what $1.00 rattle cans at Lowes are for ............GT350 if for no other reason the depreciation has already been absorbed and it's available for purchase 'today'. I'm assuming you're talking about 'MY17 or MY18 right? The Mach1 is what the PP2 should have been from day 1 but Ford was too damn cheap and blind/oblivious to consumer preferences to equip it properly. If Ford prices the Mach1 north of 53k then it absolutely no contest, GT350.
I already bought a Mach 1 back in 2019. It has this weird 'bar' emblem and says Camaro on the side, though. $38,500 including 4% tax (MSRP 45,000)