The 85-89 has the MAF 90-92 has the speed density. 85-88 has the 9th injector 89 eliminated it but kept the MAF. The 9th injector can be deleted in all the years you just need to have the chip programmed for it. 89 started with the VATS so if you go with one of those computers/chips you need to program around that. As far as which is best that is always the debate and can be your choice. The Speed density is faster and cleaner to set up. You can have a chip programmed around it. Just remember that at times you may have to send the chip back a couple times to get it right if you do any mods. MAF is more adaptable to the performance up-grades, and if you get the granitelli mass air flow sensor it has a adjustable pot right on it.