I'm just being an asshole anon, sorry. For a trip with the bros, I'd go anywhere with good hiking and walkable cities. I feel like that just makes things logistically easier for larger groups of people (and anyone really) and will significantly reduce tensions should they form. Places that fit the bill are probably most big European and Japanese cities. Easy, beautiful, great transportation. And like the other anon said SEA is great for nature and IMO the cities are really cool and fun, although if you're a pussy that's afraid of a few bad smells and mystery street meats then it will suck. Slightly more adventurous than Japan/Europe but still way safer than most shitty North American cities.
Traveling in a large group just generally sounds like a nightmare for me. Just make sure your friends are all cool with splitting up if need be and you guys should be good.