Motor voltage for 6WD rover?

Hi everyone.  Brand-new member, and first post.  My question is, what voltage would you recommend for the drive motors on a 6WD robot?

Here's the background.  My goal is to create a 6WD, 4-wheel steeering, rover robot similar to the Mars Curiosity rover.  Size will be roughly 18 inches square, 12 inches tall.  End-state is to have it run autonomously from an Arduino board; I might make it RC as an intermediate stage, and possibly switchable between RC and self-control as the final stage.  To keep things simple, I'd like to run everything off one battery - aka, one voltage.  So, battery-wise, it appears my options are 6V, 7.2V, 12V.  Motors seem to be mainly 6V or 12V, but I have found a few 7.2V.  Using 7.2V appeals to be because then I could use the same batteries & chargers as my RC cars; drawback is that 7.2V battery packs don't have long duration.  (I'd like this thing to roam around my yard for 1-2 hours if possible.)  I guess I could use more than one, in parallel.  And servos, as near as I can tell, like 4.8V-6V.   If I go 6V or 12V, then I could probably find a larger sealed lead-acid battery for longer life; of course then I would need a dedicated charger...  So, I guess I'm looking for the "best compromise". 

You can run all motors and

You can run all motors and servos rated 6V at 7,2V, it will shorten their lifespan, but it’s possible.

You can also use some 6V power regulators (LM7806) to bring the 7,2V down to 6V.

As for the battery there are 10Ah LiPo batteries in the market.