It really depends on the venue and your position — I own both cards and omnis, and I now keep a list of venues and which ones to use where. (The tl;dr is "If it sounds really great to your ears, it's probably good with omnis," but even then YMMV.)
I'll second what Mr. Fender said above, that cards are in general more resilient in lots of situations, so if you're only going to own one set, they're probably better. Though I would not go with the Core Sound Low-Cost Cardioids, which I used for years and which are both very trebly and fairly fragile. CA-14 and AT853 cards are both sturdier and have much fuller sound.