I'm a midcap kinda guy myself. The ones out nowadays are very reasonably priced, so it's not expensive to fill a vest with 8 or 10 mags. That's about 1000 rounds, which is more than enough for a full day (unless you're an LMG gunner). For a smaller or more tactical game, alls you gots to do is load them with 30 rounds and they're just as good as realcaps.
That being said, my first few mags were hicaps just because it was cheaper, and I didn't need to have an LBV. For new guys or somebody on a budget, hicaps are a good way to increase carrying capacity. The single 70-rd mag you got with that AK47-S isn't gonna last long, but the 600 round hicap will.