It would be EFIlive or HPTuners, Diablo and LS1 Edit are out dated and are limited on features. EFI and HP are really similar as I've used both. I'm really not sure how much if any you can change competitive driving mode,active handling, or HUD, but the rest can be modified fairly easily. Personally I'd recommend EFIlive because I like the layout and it was originally designed for the LS1 and Duramax so it has a few more features for those PCMs. HP was created to be a complete tuning software with more coverage, so it wasn't as focused on just the LS1 cars, but its a very complete "tuning" software ie engine mods.