If you're looking for something RF driven, I've heard @Drbretto rave about the AA Drill enough that it make me want to try it, and ImmEng has a drill option as well.
Do keep in mind that my experience with mining prior to trying the drill was with pickaxes and shovels for manual and BC quarries for mass production, so I may not have the best perspective on things, but here's the case for them:
It's early game enough to be the first main goal once you're diamond-ready. The 3x3 and first two speed upgrades are all done with easy to obtain early game ingredients and that's good enough that I haven't even bothered upgrading any further. The only thing I'd like to have added is the fortune upgrade, but I tend to just mine what I need when I need it rather quickly and move on.
The two things I like most about it, beyond the 3x3 capability, is that it runs off of RF, so it's infinitely rechargeable, and it breaks dirt and rock like you have the right tool. This makes tunneling through stone and gravel a breeze, and leaving behing a 3x3 tunnel is so much nicer to look at than a 12 mile 2x1 tunnel I used to leave. That sounds superfluous, but you have to try it to see the difference. I will never go back.