For just a normal hunting rifle used at normal hunting ranges (0-300yds) all you need is the regular 0-MOA base. There's no need for a 20-MOA base unless you foresee regular long range (500yd+) shooting in your future.

There are several good brands of one-piece picatinny bases out there, but I recommend EGW as a good option for a reasonable price. Just make sure the base says it fits these criteria...
- It must be for a Savage long action.
- It must be for a "round rear" AccuTrigger receiver.