I like both, but if I could only have one or the other I'd go with the rack. I used a Triaxis 50/50 rig for many many years and it was very hard to beat for versatility. Especially in the bar circuit.............
Man, it is a tough call. I usually end up with a head in a rack with other stuff so it's a moot point at that stage of the game. Taht being said, I recently reconstructed my rack rig and not only does it sound fucking sick, I can dial all the presets for different guitars. The versatility is very hard to beat there.