Have a automatic level sorter. I don't think it's fair for ^lvl 39's to be battling lvl32's^ or, in my case, my lvl 24/25's to be facing a lvl 29, and who knows what his other mogas were (he quit the battle).
In my experience, the best way to do this is to match up people with their highest moga's level (if they have only 1 high level moga, that's their problem for not training evenly/catching high leveled mogas), but maybe with a +/- range of 2 or 3 at most because otherwise it might be hard to find pairings in, say, the mid level 40's or 30's.