Yeah I have been to Oshawa 20+ times and Mississauga twice. Oshawa has an awesome atmosphere. Never been to the Hamilton arena
Speaking from AHL experience. Hamilton is awesome when they fill the lower bowl. Used to happen all the time when the Marlies came to town and usually they open up more beer lines. I would expect games vs Niagara, Missisauga, Guelph, London and Kitchener to draw better crowds. This gets compounded if it's a weekend game and the Bulldogs often had $3 beer Fridays.
However, if you get a weekday game vs a far away stinker team (I vividly recall a Hamilton vs San Antonio game on a Thursday) it's awful and like a morgue. 2000 in a 17,000 seater is no fun. Games vs the likes of Ottawa, North Bay, SSM, Sudbury and Barrie, I'd probably steer away from.
If Oshawa and Missisauga are closer targets (and it sounds like they are) I would not advise getting Hamilton season tickets. I'd opt for a flex 10 pack, if that. Realistically, you are never going to have a problem finding tickets for a game in Hamilton, so the need for seasons to keep your seat isn't there. When the Bulldogs do sellout the lower bowl, the usually do open up part of the upper bowl, usually about 50% of the time (really it depends on how fast they sold out). Realistically too, if Mississauga and Oshawa are in the equation, Hamilton probably won't be given Toronto traffic.