Most common subwoofer input?

RCA is probably the most common hookup. To get the sonic characteristics of your power amp you would run speaker cable to the high level input on the sub. There is no need to run speaker cable back there if you go that route, you can tap into one of your rears. Having a biwire speaker terminal and using jumpers will be the easiest way to go, then jump from a rear to the sub...or run the speaker wire to the sub first then jump over to a rear. Ahhhh, what the heck, run the rca.

If you have a designated "sub out" on a receiver that's all you need, just 1 RCA. Using a 2 channel stereo receiver or amp you will need a left and a right coming from a line level output. I'm not sure what you are running for equipment, if it is older with no "line level out" or "main out" you may have to go with my first suggestion and use speaker cable directly to your sub's high level input, then jump over to your speakers.
Hope that helps...good luck

No, I wouldn't build RCA and speaker cable for each purpose. Use one or the other. I doubt very much you would even hear a difference between the two connections, I wouldn't stress yourself out too much. To make it simple just run 1 RCA behind the wall or through the floor joists and you are done.