Knowing what extras you are going to use along with the basic engine management. Do you want to use coil on plug, EFI, EZ EFI, extra boost, traction control, etc. If undecided in any of these make sure the system will support second choice items like distributor and coil, carb(s) etc. I have and several others have the FAST system. There are may extras you can consider using. Go to the web sites and investigate their systems and installation guides etc. Make sure with the company that sells what you decide on, contacts in your area and sites for physical help with problems that will come up. Talk with installers of the system(s) you are looking at and ask questions about their system and what you want it to do. If there are none in your immediate area talk to the tech dept.
Naming the systems is easy, getting it to do the things you want may be another matter. After talking to several company's you will begin to see what the limitations of the system are, or if it covers things you will never ever use, and whether it is right for you.
I got lucky and was offered a second hand unit that was not out of date and saved a ton of money. Check on the installers credentials with the company and any problems they have had with the system(or installer) you choose.
Bill