We test drove a Marathon on a hot day and used the inverter and 2 cruise airs. We were comfortable for the duration of the test drive but, admittedly, we didn't spend all day travelling.

However, our Liberty has OTR air and, even on a hot day, you can chill the bus down to a point where your teeth will chatter.

If you really want it cold in the bus, regardless of the outside temps, OTR air conditioning is probably for you.

There are, of course, other mechanical and maintenance considerations.

In the long run, it's probably beneficial to keep your options open in order to give yourself as much of a selection as possible. To borrow a quote, "the used bus factory is closed."

Hope you find the right bus for you and that you are ultimately as happy with it as we are with our Liberty.