TG and Kleen make good points about the Body British of the T-bars. The Body British on T-bars when going astronomically heavy depends heavily on your quads, glutes and lower back, especially the lower back. The stronger your lower back, the more force you can produce on an upward sway Body British (quads also help create upward momentum, keep you from collapsing, to maintain the knee bend and the glutes are least taxed (mostly because they're so inherently strong), but also assist with the body British) so we have two arguments here.
Db Rows = more isolated lat/mid back strength; though some lower back body British can still be exerted. The only "PERFECT" One arm Db row form I've EVER seen are from women who only pull 15-20lbs and the body remains 100% still. I hardly see men pulling truly heavy weight without some form of body jerking to some minute extent, so I'd give the one arm Db rows a 3-5% Body British margin.
T-Rows = Could be seen as more of an overall strength exercise, liken to the dead lift, but to a much lesser extent, due to the many muscle groups involved to "successfully" execute Body British. I'd give T-Bars a 25-35% Body British Margin. You can practically T-row with your quads if you generate enough upward momentum. So, although you can cheat the hell out of the T-bars, technically, you need to be strong enough to effectively cheat. You can't cheat T-bars like you can BB curls, you can't create THAT much momentum and hyper-extend your torso parallel to the ground (like freaking Arnold).
So, due to the Body British brought up by TG and Kleen, I'm a bit conflicted about my original vote [t-bars], but I could logistically justify either one, body British and all.