Lower C rated batteries are more meant for low current draw applications such as crawlers and lightweight buggies. The C rating is basically how much punch the battery can deliver by way of delivering amperage. Think of it as a bottle of soda. The larger the neck of the bottle, the faster you can pour out the contents.
But basically, the higher C rating, the better the quality of the battery - in theory. As
@Greywolf74 has found in his Comparing LiPo's thread in the electronics forum, the advertised C rating kinda means diddly squat. His test results have shown that the best Lipo's for the money are Liperior, CNHL, and Zippy.
The mAh (milliamps/hour) is how much capacity the battery has. Think of this as the size of the bottle. So the larger the mAh rating, the longer you can run your RC before hitting LVC (low voltage cutoff). You never want to run a LiPo battery below 3 volts per cell. Doing so will degrade the cell(s) and hurt your battery's performance over time.
There are numerous videos, web pages, etc that explain how to properly charge, store, and care for your LiPo batteries. I suggest you spend a couple hours digesting as much info as you can before you go any further. Then come back with any questions you need answers for.
As for your question, I'd get the highest C rating and highest mAh battery you can afford that fits in your rig. 50c is ok for a basher, but more is better
Oh, if you go too low on the C rating, you will notice voltage drop when hitting the throttle on your RC. That is because when you accelerate, your RC draws more current (amperage) from the battery. If the C rating isn't high enough to deliver the required load, the voltage will take a hit, and you will notice your battery will heat up. Heat in any electronic device is undesirable.
