depends on what you want to get out of your truck.
If I had the extra $$ I would flash my PCM and get the VEC, so you get the benifits of both...but if I had to ONLY choose 1, then it depends on how involved you want to get.
The VEC has no safety...so if you dont know what your doing..BOOM
Flash is a well tested fuel and timing map(s).
If you want to do the vec, I would make sure I have many things before playing with it....Wideband(s), Data loggers, timing logging, knock -logging, injector cycles, etc...
-Red