Boeing 737 all the way, the NG (600-700-800-900) are even better. Its simple, can fly from region to region, can even fly long range to like places in hawaii from the center of north america.
In real life, its even simpler for maintenance, operating costs etc.
The 737 is currently one of the only planes that actually makes money for the airlines, hence why Southwest has 100% 737s. However, this is a virtual airline-who am I kidding, I'd still pick 737s
Reasonable choice: 737NG (with BBJ for long range work)
Unreasonable choice: Tu-144 for atlantic service Tu-114 for long range (more economical than a jet!) Fokker 100 for short range Tu-2x4 for medium range