IMO, that's up to you. The general hub would have more traffic, but the niche specific would be more targetted. Factor in the time of updating multiple hubs versus just one.
Honestly, I've seen it done both ways. If it were me and I'd decide what kind of advertisers I'd like to use as my main income source and build a gameplan from that. Based on that theory, things to think about are how many niches does my main advertiser have. Do I want to market ALL of those niches. Do I want to stick to a couple key niches. Instead of 1 or 2 advertisers do I want to market only a couple of niches from multiple sponsors and build a couple of hubs that tie into those niches. Etc...
Good luck with whatever you decide
