I have a set of Gen6 502s set up with carbs, and a pair of 502 MAG MPI sets. I question the reliability of the MPI systems. I can not have a computer glitch shut me off. So I am leaning twards keeping the carb set for reliability unless I am missing out on substancial HP.

The odds of something happening to the efi and leaving you stranded is next to nothing. The sensors rarely go bad. If they do, the ecm will use a default value so the engine will continue to run. It may not run great, but it will run. I can count on my fingers how many bad sensors and ecms I have seen.
It will cost more and is harder to tune an efi engine. The payoff is better economy, drivability, protection (detonation control) and power.
The carb is pretty simple. If you have fuel and spark, it pretty much has to run.
I think resale will be better with efi when it comes time to sell. Most want efi engines. EFI accounts for about 98% of the engines I now build. I went for a stretch of almost 5 years without building one carb engine.
Do yourself a favor and tune the engine on the dyno no matter which way you go (especially if you go with efi). You will have a better end result.
Eddie

Is there a big HP difference when you tune them both?
I have given up paying incompetant local mechanics that I have had dealings with in the past, and being that I will be the new mechanic, feel a bit more comfy with carbs, as long as I am not sacrificing too much. I have a old wellcract cat and 75-80mph is fine for me and the family. Blew the budget on new 502's after marina destroyed the 454's and went under, so no INS just small claims. Thanks AJ Marine! If all shops operated like yours and Brets It would be a no-brainer. Thanks for the advise YP.

I converted mine from carb to EFI using all used parts. I learned alot, and now it starts everytime, idles perfect and burns about 80% the fuel it used too. I will never go back to carbs.