Probably better to use the 'Truck' profile, but i really don't think it will matter too much either way as both the options are quite customizable. Provided your bus's details for dimensions, weight etc can be entered it probably doesn't matter in the technical sense, the unit will route you around low overpasses, away from narrow streets and the like. The difference may be in some countries that, for instance, certain GVM freighter trucks are banned from some roads whereas same weight passenger buses are not. I'd think that if length [determining turning circle] is a factor in narrow city streets/small roundabouts etc then it doesn't matter whether it's a truck, bus, RV or Army DUKW, it's the size that counts [ask any Barmaid in any pub in the world about that ].

Of course Garmin and their map providers take absolutely no responsibility for the use of their hardware and software anyway. It's up to the user to determine if the vehicle is used legally in any given situation.