We need a new AC recovery machine.  Which is a good one, and why?

What model or size of machine do we need to use for mainly farm tractors, combines, sprayers, windrowers, and trucks? 

We don't usually need to be able to vacuum down semi's with sleepers, or RV's, which I presume require a lot bigger capacity machine?  What happens if the machine is not large enough to hold the amount of coolant a system requires?

How long of a hose do you typically need to be able to get up to the ports on a combine?

Any advice is appreciated......