There are much more choices for 50-100 seats aircrafts than 100+ seats aircrafts, with types ranging from turboprop to wing-mounted jets to fuselage-mounted jets, from 4-abreast to 6-abreast Economy Class, from low wing design to high wing design, from baggage space placed after the passenger cabin to the space placed between the cockpit & the passenger cabin to the space placed below the cabin like the large jets.
There are 10 main series of 50-100 passengers aircrafts.
1. BAe Jetstream 146 of high wing quadjet design. This design allows very low land clearance, so only the ladders installed in the aircraft are needed for passenger flow. Its quadjet design allows high MTOW (maximum takeoff weight) & high payload / MTOW ratio, thus making it ideal for small sized freighter (there is freighter version of the aircraft.) This also allows takeoff at very short runways, say 1200m.
But it is the least economical regional jet.
Its cabin is so wide that it is configured as 5-abreast or 6-abreast design, thus providing less privacy & comfort compared to most other regional jets.
2. BAe Avro RJ of wing-mounted twinjet design with high places tailwing. Like Jetstream 146, its cabin is configured as 5-abreast or 6-abreast design, and is not quite comfortable.
But it is more economical to run & quiter than fuselage-mounted jets.
3. BAe ATP 68 seat twin turboprop of low wing design. Such turboprops fly slower, but gives much lower cost than jets for trips less than 500km.
But it is much noisier than jets.
4. Canadair CRJ of low wing design & fuselage-mounted engines. It is the most popular regional jet in Western world because of good economy, good comfort due to 4-abreast design, and excellent takeoff performance of only 1200m runway.
5. Canadair Q series twin turboprop of low wing design. It offers quieter trip than conventional turboprops as the series letter Q (quite) suggests.
6. Embraer 170/175/190/195 of low wing design & wing-mounted engines. It is the newest regional jet series in the world, with comfortable 4-abreast cabin, and cargo space placed below the passenger cabin like the large jets for more cargo & baggage capacity. This also provides very quite & smooth trip.
But the wing-mounted engines design makes the land clearance of the aircraft very high, so passengers cannot board the aircraft without external ladders provided by airports.
Its takeoff performance is very poor compared to other regional jets, needs 2000m runway length like large single aisle jets, thus making its operation very constrictive.
7. Fokker F70/F85/F100 of low wing fuselage-mounted engines. It was the most popular regional jet in the world before the collapse of Fokker, because of good economy in operation. It features 5-abreast design, which is not as comfortable as 4-abreast design.
8. Boeing B717 of low wing fuselage fuselage-mounted engines. It is the most direct successor of Fokker jets after the collapse of Fokker, with 5-abreast design & fuselage mounted engines. It has cargo space placed below the passenger cabin.
9. ATR 42/72 of high wing twin turboprop design. This allows good takeoff performace, only 1200m runway is needed. This also offers low ground clearance, hence passengers can board the aircraft via the ladders mounted on the aircraft.
It has very special design of baggage space being placed between the cockpit & passenger cabin.
It also features maintenance-free dampers between the passenger cabin & the main body, and speakers at the engines to reduce noise, thus providing jet-like quiteness & smoothness with excellent economy especially for short haul routes.
10. Xian Aircraft Company (XAC) MA60 of high wing quad turboprop design. It is actually a Chinese version of a Soviet quad turboprop, which is very common in Soviet & East Europe. It offers excellent takeoff performance due to quad turboprop design, but is not comfortable.