Personally, I don't like hi-caps because it detracts from the 'realism' of airsoft. I like airsoft over paintball because my Classic Army M4 doesn't resemble a super soaker. I'd like it to look and function as realistically as airsoft would allow; including reloading.
Hi-cap rattling pisses every mil-sim player out there. I'd imagine non mil-sim players would also be a little ... turned off by this?
Hi-caps make load-bearing vests kinda redundant. 1 M4 hi-cap = 300rds. Most vets/rigs have 3 pockets. So thats around 900 BBs (double that if the pockets are larger). I don't know how you guys play but I rarely use up even 300 rounds in half a day of light skirmishing.
I only use hi-caps on my m249. The only other hi-caps I have came with the gun.
Having asserted my position on hi-caps, I don't neccessarily like real-caps either.
I think low-caps are the best. Low-caps usually have a little more than double the real guns capacity. Given the much lower accuraccy of airsoft guns, I think the additional payload is a reasonable comprimise. Low-caps are also more durable, less expensive (per unit

), don't rattle, and don't require winding.
Long live low-caps