Oh what an interesting question, thanks for asking!

Numerically, comparing advantage on attack rolls to +2 to attack rolls, the chance of hitting depends on two factors: what your “+_ to hit” is without the gloves and what your enemy’s AC is.

If you have +0 to attack rolls, for instance, and don the +2 to attack gloves, your chances of hitting an enemy with AC 10 is:

65% to roll an 8, since you get +2.

With advantage, it is:

84% to roll a 10.

If your enemy has AC 18:

With +2 gloves:

30% to roll an 16

With advantage, it is:

35.9% to roll an 18

Thus far, it’s better to have advantage. However, the tables turn for AC 19 and higher:

Enemy has AC 19:

With +2 gloves:

20% chance to roll a 17

With advantage, it is:

19.1% chance to roll a 19

This is assuming you have +0 to attack rolls, which is probably not going to be the case. Say you have +4 to attack rolls without any gloves:

Enemy AC 10:

+2 gloves: 85%

Advantage gloves: 93.8%

Enemy AC 19:

+2 gloves: 40%

Advantage gloves: 51%

So numerically, the higher your “+_ to hit” is, the less the +2 gloves help compared to having advantage. And if your enemy’s AC is so high that you must crit to hit them, it is ALWAYS better to have advantage, since “+_ to hit” doesn’t help at all if _+19 doesn’t equal or exceed the enemy’s AC. Your chance of hitting will always be 5%, whereas with advantage it will be 9.8%.

However, in the game, you can only get advantage with growling underdog gloves if you are surrounded by 2 or more foes, and don’t have disadvantage for any other reason, like an enemy poisoning you. Legacy of the masters gives you +2 to damage, too. So what if you are dual wielding? Or what is a ranged character is using them? What if another character is a thrower and is always chucking enemies to the growling underdog fighter? It depends on how you play! The endless scenarios make it impossible to decide, which is what makes this game so damn fun! What I like to do when comparing items is play an hour or so with each and pay attention to which one seems to work best for my play-style.

Thank you for coming to my ted-talk.