Both are excellent choices, and both capture a whole lot of what I like about Ampegs. I use a VT Deluxe with my Ampegs for distortion at low volumes all the time, even the tube amps. I don't have the PF500 but I have a Micro VR and it's amazing, and the PF500 is just a little more amazing than the Micro VR (SVT 7 Pro is king, though).
So pros and cons....
VT Pros:
--Cheaper
--Wider range of distorted sounds
VT Cons:
--Knobs are very sensitive and hard to adjust on the fly
--No power amp
--No DI, although it can be modded for one by
Putnam Guitars - Custom guitars mods amps pedals effects speakers and it sounds excellent
PF500 Pros:
--Light
--Has a power amp
--Has a very versatile and easy to use EQ that sounds great set flat and even better once you tweak it a little
--Has a DI
PF500 Cons:
--Doesn't have as wide a range for distorted sounds as the VT...it'll do a nice mild grind, but not full on angry cranked tube distortion like the VT
--Cheap but still a couple hundy more than the VT
Obviously the cheapest way to get your feet wet is with the VT. But if you don't need all the distortion a VT can give you, and you prefer one-box solutions rather than carrying an amp and a pedal, the PF500 is the way to go.
