I prefer the minigames for a few reasons:
1. 25 minute days means things happen quicker.
2. The lack of trans-Atlantic/Pacific routes means no massive airlines with ridiculous F/C demand making ridiculous margins and crushing the little guys.
3. Slots are actually available. Most of the major airports with major international demand would be locked up at this point.
4. Used aircraft availability. Seems that we have a whole world worth of aircraft versus just 200 airlines worth. This means no 2+ year backlog for new aircraft because what you need is usually available used, even A320 and B737.
5. Alliances are more strategic. You can't have 25 airlines based in the US in the same alliance because you'll constantly be running into each other, especially when bases are considered.
6. Players are using appropriate aircraft (so it seems), thanks to the competition and new pax algorithm. Iksu was flying 16x daily with Dash-8 (part of an experiment) on 1500 pax routes and failed. Those flying ~125 seaters and myself flying 90 seat CRJs remain successful. The larger jets seem to be beating the smaller props on routes that props shouldn't be flying IRL. However, if you want to get a new Dash-8 you can get it in a few months versus a few years--historically the massive international legacy-type carriers would have the Dash-8 production line locked up for years.
Interestingly enough, the big jets like the B777 and A340 have gone out of production due to lack of demand. I think another North American Challenge would be interesting if players could only base in North America, but could fly anywhere in the world. The competition would be/could be brutal as there would be no slot issues flying to Heathrow, for example. This means every player based at JFK would have flights to Heathrow and they would be working at putting each other into bankruptcy. With the new pax model, this excites me since you won't see Trans-Atlantic 737s flying these routes anymore. I haven't tested it out, but I assume the pax sensitivity to seat config/density has been increased so those flying the routes with premium seating should crush the high density airline.
If AI features could be enabled, I think it would be cool to have the above (base only in North America), but have a major AI competitor based at every international airport flying with existing routes with sufficient demand being flown already. So there would be a Heathrow Airlines, Syndey Airlines, etc. with enough seats on all the major international routes to North America that if someone wanted to fly international it would be an uphill battle for players.
Those are my thoughts on the next North America Challenge to increase the "challenge"
If city-based demand were enabled it would be even more interesting.