Midcap all the way.
Honestly I've never owned a hicap in my life (bought my first rifle used and it didn't come with any mags). I've used them/borrowed them before but all I own are mid (120rds) and lowcaps (75rds) and I see no reason to switch. Just buy them up slowly, it looks like you have a hicap judging from what appears to be a small wheel at the bottom of your rifle so assuming about 300 BB's plus lets say 2 midcaps to start out you've got a little less than 550 BB's in total on your loadout then slowly acquire more midcaps til you think you have a good amount.
Also, I own G&P midcaps which I love to death but that's just one case; you can choose to get those or PTS Pmags (Avoid the Magpul "Green Label" mags at all costs). Also I've seen some of the VFC Metal Midcaps which appear to be solid and pretty good mags as well.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE