[Outlaw1]

The majority of the people out there don't need aftermarket ECU's because they don't have any clue how to tune. If an inexperienced person feels the need to tune his/her own car, just be sure you're prepared to swap a blown head gasket or build a new engine. I'm not saying anyone is experienced or not experience, I'm just pointing out the obvious. I'd say most people don't understand how an S-AFC affects their tune.
As far as DSMLink vs. Megasquirt goes, DSMLink is ready to work right out of the box. It looks very user friendly. It's just a matter of tweaking fueling/timing tables for your specific needs. MegaSquirt is closer to an old school DFI. It was not built vehicle specific. You can get a ballpark tune, but it's not like starting with a bone stock Mitsu image.
Depending on how much power you want to make, an EPROM ECU with a custom chip may be the best and cheapest alternative for you. In the end, whether you're using an SEFI8LO, DFI, MegaSquirt, DSMLink or stock ECU w/S-AFC, if you understand how to manipulate the fueling/timing maps to get what you want, it doesn't matter how you get there.
Ask yourself these questions. What is my target A/F ratio? What is my target total timing? If you can't answer those questions, it's best to let someone like Shane tune it for you.