IF I had to pick one, I'd say 69 Mach 1 in any grabber color. Since I have now owned 5 Mustangs at one time or another all of them were.
In order:
94 GT Bright Blue
67 fastback 390ci
01 GT Tropic Green
05 GT Screaming Yellow
98 Cobra convertible Crystal White
The SN95 Cobra was always a dream though. I was in high school when they came out. Finally got one!