Ace force itself does not increase health, it merely deliver the level-up bonus more quickly by boosting exp-gain-rate.
Here is the benefit of lvl-up
1 > 2: +10
2 > 3: +20
3 > 4: +30
4 > 5: +40
5 > 6: +50
Also, you get damage reduction of (current lvl-1)x5.
It's easier to understand if you think it as you start from lvl 0 and max up at lvl 5, where each lvl reduces damage input by 2.
Note that the hp bonuses are for CURRENT HP not MAX HP. There is no way to increase max other than promoting the general.
Implication: If you start from lvl 1 you can gain +150 hp maximum by level-up. Or, if you start from lvl 4, that means you get +90 max.
To compensate this you'll start with -6 damage reduction bonus if you start from lvl.4.
Analysis of Ace Forces
*Ace Forces' value increase with decreasing number of turns available. (Campaign > Conquest) Supply does the exact opposite.
*Ace Forces is only really useful on units that you expect will die before they reach lvl 6, assuming they don't have the skill.
Ace Forces VS Supply
If I had to choose between the two, I'd generally go for Supply. In general you are guaranteed AT LEAST 11 turns in any campaign mission, which means you'll eventually regain +80 health. Ace forces gives 80% exp bonus, which means it hastens lvl-up bonus by less than 200%. Do the simplified math: +150/2= +75. So AT BEST, you get potential of +75 from Ace Forces.
SUPPLY + ACE FORCES > SUPPLY > ACE FORCES
