Having been to every CFL stadium save for Tim Hortons and TD Place, I guess I judge the stadiums a bit differently. As far as pure impressiveness of the facility coupled with size, Commonwealth is definitely #1, but as mentioned it lacks intimacy and atmosphere. This is really too bad, because Edmonton has consistently been one of the most loyal fanbases in the league and this city loves the Eskimos. Leading the league in attendance nearly every single year and the stadium looks half empty, and the atmosphere when you're at a game there is not great, even when it's full.
It would be wonderful hypothetically if we could have a smaller, football-specific stadium for the Eskimos and then I think the Eskimos faithful would be more appreciated across the league and the country (of course this is just dreaming, Commonwealth is a great stadium and doesn't need to go at all).
I was very impressed by Investors Group Field, as far as I'm concerned it's the perfect CFL stadium. It is modern, aesthetically pleasing (for me anyway), the right size for the CFL, has a great atmosphere and it just does something for me that Commonwealth can't. BC Place has that same pizzazz, but not the atmosphere of Winnipeg (though it CAN have that atmosphere as I witnessed at the 2011 GC).
McMahon Stadium is absolutely atrocious, but has great sightlines and (I may get some flack for this) a better atmosphere than Commonwealth, even when it's not full. A new stadium in Calgary would be a real experience.
Come to think of it, I think the Esks and Stamps fanbases are both grossly underrated in this country.
From what I've seen, TD and THF seem to fit my criteria of what I like in a stadium quite nicely, though TD Place has always looked a lot more modern and cool to me than THF (at least the new stand and exterior), but obviously I haven't been to either.
I really think the new Mosaic, when you combine the facilities aspect with the gameday experience aspect, will blow all of them out of the water. That might just be my green coloured shades though.