Depends on your budget. If your pocket is deep, go for a dezl 760 or RV 760 with a 7" screen. Great for vehicles where the unit is a further from the driver than in a car, has more features than the others. If a bit poorer, get a dezl 560, 5" screen. If you're kinda broke go for a nuvi 465 [truckie's nuvi] 4.3" screen.
If you have a few modding skills, buy a nuvi 2797 to convert to dezl 760 or RV 760, nuvi 2460 to convert to dezl 560 or nuvi 2x5W [hwid 0827] to convert to nuvi 465, be cheaper still. See this tut for 2460 to 560: [Only registered and activated users can see links. ] The same principals apply to the other 2 conversions, but best to stick with hybrid fw to be safer.
As for the profile to select, 465 has Truck, 560 has Truck or Motor Home/Caravan same as 760. All can also be in Car profile too of course. It really depends on the size of your bus whether you should select one or the other. The profiles are quite customizable as to dimensions, weight, axles etc.