IMHO you need to look at where you are (hardware) and your HP or ET goals..... and your level of comfort when going in to tweak the system yourself. Anybody that thinks they buy a BS3, XFI, etc. and all their tuning problems go away is dreaming. You need to be able to tweak certain things yourself (example; cold start, hot start, etc). If you can't or don't have someone locally at your disposal to help, it could be frustrating.
IMHO, there are chips out there now perfectly capable of controlling the EFI on 9 sec turbo Buicks..... with and without a MAF.......with wideband WOT tuning capabilities....... etc...... COP.......2-steps.....etc. so if you are 10's, 11's or 12's....... you really need to consider all the options before choosing.
With all that said.... if you go aftermarket ECU, the XFI is far and beyond the most popular system on Turbo Buicks and has the most support around here from individuals and also businesses such as Cal's..... you won't find any system on a TB with any easier support at your fingertips than the XFI.