I fly my mid-vent 75% of the time.
Std about 15%.
Vented and Xtra-vent the last 10%.
My mid is my "go-to" kite, but I bought it third after the std and full vent. I'll also use the mid a lot of the times when I should be using something else. I just love the way it handles more than the others.
Make sure to study/research the typical winds at YOUR flying locations. No question if you could only ever have 2 Rev's a std sail and full vent would be the wisest move for 99% of people. However if the winds in your area rarely go over say 12mph, then you would likely see much more use (value) from a Midvent.
I own all three (most rev fliers will own all 3, its just part of the addiction!) My full vent has seen maybe 30min of flight time in the last 6mos, but my std and mid have at least 8hrs each. The full vent just take more wind to even fly than I typically see, hoping more beach trips change that!
Welcome to the party / addiction / madness / joy of Rev flying!