Well, let me explain my "sounds dumb." I think anime over-uses its tropes, one of those being, "Little girls in roles little girls don't normally fill." This is unabashedly for the looks, since apparently there isn't a large enough anime demographic for, "watch grizzled 40-something males spy in steampunk London." It just gets under my skin after a while, because I think it's usually to the detriment of the show. Youjo Senki, probably my favorite show in the last few seasons, also suffered from it.
Anyway, as to which is better....I dunno. Abyss blows PriPri out of the water in terms of art and atmosphere. It has that distinct indie game style: pretty scenery, a sort of fantastical ambiance, but with just a hint of something deeply off about the world. PriPri has more to its plot so far, which is put together in a series of non-chronological episodes, giving us a piecemeal view of what is going on. It also has more action and some pretty dark moments. Personally I feel that PriPri started stronger but has gotten weaker, while Abyss is still growing (but yet not realizing) its potential.