My wife and I cruise on a Catalina 310. A couple feet longer and wider than your C30 but in the same ball park.
Our primary anchor is a Manson Supreme 35 pounder. Admittedly this is an oversized anchor and the 25 pounder would work for most people. We also have a danforth, a fortress and a big fisherman's storm anchor. I wrote a post about sizing anchors and rode on our blog:
Let's Talk Ground Tackle.
My recommendation is that you research the new generation anchors: Rocna, Manson Supreme, Mantus, Spade, etc. These do offer superior holding in a larger variety of bottom types. Most importantly they are generally self re-setting when you swing during tide or current shifts. But also plan to carry some of the more traditional anchors, like the danforth or even better a Fortress. Danforths have some of the highest holding strength of any of the anchors if set right.
Good luck and fair winds,
Jesse