Stabilitiey of macro vs. mega functions in 3000

I don't think you'll be seeing any difference in stability with either way with macrofunctions or megafunctions.

I'd say that by using megafunctions, you might be able to simplify your design and let the tool implement better optimizations.

Ie. instead of building an 8 bit counter with registers and 7483 4-bit adders, you can just create a 8 bit counter megafunction and be done with it.

MAX-Plus is a dead end, software wise. Altera only recommends it for legacy designs.

When I have to support a design that's been tested and deployed, I often avoid even changing Quartus version. But whenever I move to a different device, I go for the latest Quartus.

So, since you're changing device, I'd change to Quartus.