We went with the folding ratchet-type, which got from about 12" to 17" when in the down position. They tuck up under the frame & can't be seen when not in use. The main reason for them is the air conditioner we run during hot weather. I wanted to be sure it ran OK & that the unit would drain properly out the front with condensate, if it was too muggy when it was running. With the tongue jack (2000#) & the 650# rating on each rear jack, we can level the trailer for sleeping pretty easily & it's quick. Also helps to elevate the head of the bed if you have acid re-flux.
Best use I have for this is at Bonneville in August for the racing. It was in the 90's during the day & the trailer would get pretty warm in the afternoon with full sunlight & no shade. With the air running, I could get the interior temps down into the 50's if I wanted to, then at night it would cool off well enough after sunset to be good sleeping weather. A half hour of cooling before sunset was all it really needed, but that 1/2 hour was time well spent.
The jacks take a bit of time to setup, but in some cases are worth the trouble. Usually, they aren't really necessary on a level spot, but if you're building from scratch & need to use them...
