General consensus is the lower the capacity, the more reliable the magazine.
Highcaps have a tendency to not feed properly, ie: the 10 rounds and you have to wind up. I had that problem with my high-cap, and switched to midcaps. Of course, there are some highcaps that are reliabel. Regardless, in a game, a highcap tends to rattle as a result of the BBs. Pretty much not wanted by anyone.
Midcaps are relatively reliable. Some (not all) need a little oil to et the job done. My MAG 100rd SiG Series magazines required oil to function properly just because of the friction causing jamming. Again, some midcaps work flawlessly.
Lowcaps tend to be the best, out of the box, IMO. They feed in a straight line (or as straight as it can get for the type of magazine), so there's no curve like in midcaps for BBs to jam up. I haven't seen or heard anyoen complain about their low-caps not functioning properly, although sometimes people go ballistic because 1 or 2 BBs didn't feed.
For all magazines, if you decide to oil them a bit, make sure it's just that, a bit. If you over lubricate them, you get gunk in your mags. At that point you just end up hating all lifeforms because now you have to try and clean it out (and in some cases have to re-oil it properly, which is kind of a waste of oil).
Primary: Custom WE M16A3
Secondary: KWA MP9
Side: Custom WE M1911A1