If it's a choice between a Cannonball and a Mark VII, and you don't have the chance to play either, and you simply have to buy one of the two, if I were you I'd go for the Mark VII without question. I think they're great horns. I've liked every single one I've tried, never understood the hate, and although their ergonomics feel a bit different from other horns, it's nothing that wouldn't become easy and familiar with a little time. If you're buying from Reverb, you'll probably be taking it into your favorite local tech anyway, so that will help account for minor things you might not like about the setup.
Mark VIIs are also going up in value, albeit slightly, while Cannonballs probably won't for the foreseeable future. So if you end up wanting to sell it, you'll reduce your chances of taking a bath.
Mark VIIs are also going up in value, albeit slightly, while Cannonballs probably won't for the foreseeable future. So if you end up wanting to sell it, you'll reduce your chances of taking a bath.