Optimal would be the battery that gives you the most amps at full throttle, is the lightest, and is the most durable. C ratings really don't mean much. Within a given product line they do indicate batteries with a little less internal resistance generally, but across brands there is no standard for what they really mean. So optimal would be one of the top shelf batteries in a 30c rating. Everyone has their favorites, but I'm thinking Hyperion, Thunder Power, and Maxamps will be near the top of most people's lists. What's really important for performance is the weight per capacity and amps delivered. The cheaper batteries work and are fine for just getting out and enjoying your plane, but they are heavier and simply won't deliver the same amps that the better brands will. Of course, you can have 5 Zippys for what one Thunder Power will cost, and the 5 Zippys together will probably last 3 times as long as the one Thunder Power before needing to be replaced. So it comes down to what gives you the most enjoyment out of your money spent.