For heavybag training, definitely go with traditional bag gloves. Think about it:
1) During the course of a workout you'll throw 1,000 punches, easy.
2) You don't want to injure your hands, because then you can't train.
With that in mind, here's a pop quiz:
"
How much foam do I want protecting my hands?"
a) 12oz of 2.5" thick foam
b) 4 oz of 1/2" thick foam
If you chose answer a, congratulations! You have common sense
and respect for the health of your fighting tools, a very rare combination that will serve you well.
Now, doing work on the double-end bag or focus mitts with MMA gloves might not be a terrible idea. But heavy bag work can be really punishing. Protect your tools the best you can.