In the school bus world there are four types of buses and variations within the types.
The types go up in size from small van/cut-away chassis buses to tandem axle 40' buses.
The engines range in size from small gas engines (some of the really small buses have a V-6 gas engine in them) to 450+ HP Cummins 855 Big Cam engines with many different choices in between.
Depending upon how you are going to use your bus, where you are going to use and drive your bus, and how often you are going to be driving your bus will have some sort of impact upon what will be the best bus choice for you. Be advised, there is no one perfect bus. Which is why there are so very many variations.
Many of the choices are the Ford vs. Chevy vs. Dodge sort of prejudices that most of the time don't make a lot of sense. For instance, I really have never liked Blue Bird buses and wouldn't choose one unless it was too good to pass up.
As far as engines are concerned, an inline diesel engine will produce better power on less fuel than any sort of V-type engine, even if both have the same HP and torque rating.
I personally do not like Cat, Mercedes-Benz, and Brazilian Ford diesel engines. It isn't that they made bad engines so much as parts and service for them tends to be needed more often. It always seems to cost a lot more to purchase the parts for them. It can also be very difficult to find a willing service tech who will work on them at a reasonable price.
Once you determined all of the necessary parameters for what you will need in a bus we all will be in a better position to make specific recommendations for you.
Good luck and happy trails to you!
