I'm torn between crab and armadillo, but I think I'll vote armadillo.

I don't think dog armor is really going to be that useful outside of just looking cool on your wolf. It probably won't save them from lava or make them actually that helpful in combat. Granted, dog drip is cool, but it's not like wolves are suddenly gonna become viable because of it.

In contrast, the crab claw is much more useful. From my experience playing modded MC, extra range is so so so nice for building. Even 2 blocks of extra range would probably be great.

But with all that being said, I'm thinking I'll still voting armadillo for a couple of reasons:

• This isn't how I want to see a range extender implemented. This is the kind of thing that could be midgame or even endgame structure loot just because of its utility, but instead it's… a drop from a random mangrove swamp mob? It seems like a massive waste of an opportunity.
• Armadillos are the best mob from an ambience perspective. Savannas desperately need some more life, and even if ostriches and termites will be coming eventually, armadillos are a great addition for that. If they roll/unroll, especially if in response to the player getting close, it'll add a lot of movement to the savanna. Meanwhile, mangrove swamps are already much more visually interesting than normal swamps, so I don't get making the quality gap even further.