Some people think this would be a no-brainer, but I've actually not been as sure. If it's an adventure game series, chances are you'll play as someone who solves puzzles with absurd gadgets and items. However, it also means you'll likely engage in conversation with the other characters and such.
But Wallace hasn't been great at this. Often in the shorts and movies, he's the one bumbling about thinking everything's fine, whereas Grommit slowly unravels the mystery.
Of course, since conversation is a bit of a must, I don't think we'll see too much of Grommit grilling passerby about the devious catburglar that passed through the night before. There's certainly a tradeoff, and it's not as clear cut as Sam vs Max.
(if devs can freely answer this, the thread will be short. Otherwise, the topic's open to speculation)