Which Bus is the fastest in GTAV? When I'm playing with friends, it takes me too long to get to waypoints in the current bus I use
There's really only 3 busses in the game, and their speeds all top out at 540 - the generic "Bus" slightly edging out the other two in breaking. The smaller Rental Shuttle Bus / Tourbus are slightly faster at 590. There is also the Police Prison Bus, but that is slower than all the others at 490.
If you need to get places quicker, I'd suggest something that isn't a bus (Unless some mission/heist requires a bus?). They are big and heavy, but not fast.