Good hicaps (TM armalite for example) are by far the most reliable mags I have ever used. They feed even in 30+ round/second guns where even 68rnd mags can have issues, and I find I can get around 100rnds out on semi or 200rnds in auto bursts. If your hicap only fires 10 shots then its broken, you said JG, nuff said there.
They rattle and are totally unrealistic, but they are incredibly reliable.
I use MAG plastic 110rnd midcaps, have 16 of them for my rig, use STAR 30rnd realcaps in games that require it, have 20 of those. I would use King Arms 68rnd metal lowcaps but they don't feed at all in the ICS guns I have tested them in so I can't use em.
I have had lots of issues with STAR midcaps (90-120rnds) but their realcaps (20-30rnds) work great. I have had no issues with any MAG products at all and they feed faster than any other brand of midcap I have tried. TM is the most reliable, period, but also quite expensive. I had MAGPUL 120rnd PMAG's before (the real ones, not the "green line" ones made by STAR) and they where amazing, better than MAG midcaps but at 2-4x the price I prefer MAG.