Swarmkeeper
Hero
To quantify this a bit, I went out to Kobold Fight Club
For the party, I entered:
3 level 8 PCs
2 level 7 PCs
4 level 2 NPCs (same results whether level 1, 2, or 3)
2 Frost Giants are deemed a Hard encounter with adjusted XP of 7800
3 Hill Giants are deemed a Hard encounter with adjusted XP of 8100
So, by this metric, both are deemed a Hard encounter with a slight edge for difficulty given to the 3 Hill Giants
For funsies:
Adding 1 ice memphit to the enemy mix makes the 2 Frost Giant encounter Deadly (adjusted XP 11,850) while 3 Hill Giants are still just a Hard encounter (adjusted XP 8,250)
So, yeah, there's that.
For the party, I entered:
3 level 8 PCs
2 level 7 PCs
4 level 2 NPCs (same results whether level 1, 2, or 3)
2 Frost Giants are deemed a Hard encounter with adjusted XP of 7800
3 Hill Giants are deemed a Hard encounter with adjusted XP of 8100
So, by this metric, both are deemed a Hard encounter with a slight edge for difficulty given to the 3 Hill Giants
For funsies:
Adding 1 ice memphit to the enemy mix makes the 2 Frost Giant encounter Deadly (adjusted XP 11,850) while 3 Hill Giants are still just a Hard encounter (adjusted XP 8,250)
So, yeah, there's that.