I use a spreadsheet that has all of the ilevels per slot, updated by running a perl script about once a day. I generally check that spreadsheet for the slot (not that most leveling gear is any good to me, with full heirlooms I vendor almost everything yet somehow can't get a full set of agility rings for my hunters to save their lives). I then give it to whoever has the biggest upgrade (or, if they are all the same as they often are from quest gear, the one that had the lowest dps on the most recent boss).

There WAS an addon that helped with this (it would put the ilevel of each toon for that slot into the item tooltip) but I haven't seen anyone mention it in years and it probably no longer exists.

As for equipping If you wanted to be fancy I suppose you could loot the item from the master, drag it into the jamba item box, trade the item to the slave and then trigger jamba item-use.