I would go with Mending; at least in my case I do not need Infinity because I use my sword to kill most skeletons (e.g. ambush them around a corner) and do not use my bow on much else, which I recently confirmed during a test playthough on a mod I was finishing; I did not put Infinity on my bow and started out with a stack of arrows - and ended up with a stack, with only a couple dozen uses on my bow (only Power V, while I normally also use Infinity and Unbreaking III), compared to 400 on my sword and about 60 skeletons killed, which drop an average of one arrow each so that's more than twice as many arrows as I used (I did not pick all of them up). Looting, which I did not use, can also use used to increase the average drop rate to 2.5 per skeleton (0-5 vs 0-2 each).
Actually, even Mending is a bit overkill in that case; 24 uses per day and 1540 uses with Unbreaking III results in one repair every 64 days and an overall lifetime of 449 days (initial bow + 6 repairs); as it is I often repair my bow about once a month using half-damaged bows dropped by skeletons so that is about right (I play in an older version so renaming an item on the anvil lets you repair it indefinitely, with a Power V, Infinity, Unbreaking III bow costing 31 levels to repair, about the same as the final repair possible in 1.8+, 33 levels).
I might use a bow more often in 1.9+ but most of the time when I encounter a skeleton I practically run into them while lighting up a cave; I've played a bit in 1.9+ and I did not really notice much of a difference, aside from being a bit harder to shoot with a bow due to their strafing (missed shots do not necessarily count as using more arrows since you can pick them up but your bow does wear out faster so this is another plus to Mending).