I honestly couldn't choose. My mare Penny's awesome, although she can be a pill when she wants to be ;p such as on some day's i'l go on a trail ride and she decides that, no her brakes don't work today, lol. But she's never kicked/bitten/bucked/pigrooted/bolted etc etc since the day I brought her home. I've never noticed her being moody or such when on heat, although lately she's been difficult, but I think that's jealousy coz i'm giving most of my attention to my other horse.
My gelding's a sweetie, but a bit more nervy than my mare (thats coz he's young and a tb though), I still haven't sussed his personality out completely, as i've only had him a few months, so I can't really compare.
I'd say that both have their pro's and con's, it depends on personal preference. Me? I'd have both