I'd say it depends on two things;
1. What is the goal you have for your recording, and
2. What does the venue sound like?
Regarding 1, if your goal is to minimize the ambient sound (crowd, reverb, etc), then for sure run the cards since they're directional and reject off axis sound.
With regards to the venue, if it's large and boomy, then for sure you'll be happier with cards. If the room has a nice ambient sound that you'd like to capture as an integral part of the recording, then omni's.
Generally, for my own recording purposes, I never use omni's indoors except when the mics are on-stage or for situations like acoustic or chamber music where there will be minimal audience chatter and/or reverb bouncing from the walls. I might consider using omni's indoors in a perfect sounding room, but probably even then not if the music is amplified because even in the best room there will be significant reverberant sound-waves that will mess with the quality of your recording.
Outdoor is a different story and I'll use omni's since there's generally no reverb to worry about and I can get the mics way up above people's heads.