BUY THE ONE THAT STIRS YOUR LOINS AND YOUR SOUL WHEN YOU SEE IT!!
Seriously.
I bought a SG and now will be getting a TourPak. Also ended up getting a taller windshield, a more comfortable seat, heated grips, different bars, and am going to replace the sound system. BTW, the sound system sucks on both bikes. Don't get your hopes up. The stereo is easier to modify on the Ultras, FWIW.
You may end up doing some of the same things if you get an Ultra, though. I've heard about $1000 to make the TourPak quick release at a HD stealership. That probably equates to $400 to $500 at an independent shop.
I wasn't moved by the 2012 Ultras, and I loved my SG, so I wouldn't do things any differently. If you don't get get firsttimeihadsex butterflies when you see your bike-to-be, wait and see what the 2013s look like. Maybe they'll have decent sound systems by then.