Omnis are great in a great sounding room, especially close up, when there is not a lot of crowd chatter. If there is a lot of crowd chatter, cards are better at rejecting noise behind them so are generally the go to mics for audience recordings. In your case, being the artist and having more control about where to put the mics, omnis might work well the majority of the time, but it does depend on acoustics in the room and crowd noise as well.
I'd add a little bit to the above advice...your question asked 'for general purpose' use.
FWIW, I think most people, if they had to choose a single mic pickup pattern, would choose cardioids as the best general purpose mics, because they're the middle of the road in terms of directionality. This make them a versatile microphone pattern for the many different situations encountered when getting to the gig.
I agree that omni's can sound really great close-up because you're recording the natural sound of the instruments (instead of the PA), but close mic'ing imposes its own set of challenges in regards to getting good balance between all of the instruments and the vocals of a musical group. It's usually not good enough to simply put the mics in the middle of the stage and expect to get a good balanced recording because the bass might be too loud and the vocals not loud enough, or some other dynamic issue that affects the balance.
So, it's often easier to move back from the stage a little ways and let the natural projection in the room balance the sounds (for acoustic gigs) or let the soundguy worry about balancing the sound through the PA speakers. In that case, use the directionality of the cards to zero in on the sound, while rejecting the crowd as much as possible. FWIW, I've also gotten plenty of great up close recordings with cardioids in front near the stage in ORTF configuration.
In the end though, which mic is better depends entirely on how you plan to record your band and where the mics will be positioned. If the mics will be out in the audience, you'd DEFINITELY want to choose cards over omni's. If the mics will be on stage, then you'd want to consider some of the things I've stated above.