i am about half and half. i am EXTREMELY pleased with the results of my custom tune. i recently put my blower on, 42#'s, and 90mm and needed a custom tune and really wanted to try and nail it as close as possible without getting to a dyno because there arent any good tuners around here. i am LUCKY because one of my best friends is a diablo dealer and could burn me chips as much as i needed. Diablo nailed a perfect tune the first time they sent a program, 11.8:1, just like i wanted. only bad thing was they didnt remove the top speed limiter and my truck kept shutting off at 98. well, i kept bitching and it took them 4 more tries (in 3 months) but they finally got it right. i was kinda pissed cause i missed all the cool weather at the track and now i cant run cause its so hot, but at least i got it where it'll go faster than 100 now.
i'd go with diablo again if i had to. but if i was gonna spend the money and go to a dyno, i'd go with Superchips SCT or Autologic. i went with diablo cause my friend could burn them for me.