They're both worth buying, but the 7s is more "normal" and more generally useful.
(So having said that, why did I sell my 7s and keep my VI-T? Just eccentric, I guess...)
I'd like to stick up for the VI-T a bit, especially in the winding/focusing department. For many, many years the VI-T was my primary camera for shooting ballet performances (with 50/1.4 and 100/2 lenses) so that certainly should prove you can focus, fire and wind with only two hands.
I suspect the secret of my success is that my VI-T has the Canon palm grip accessory, a knurled cylindrical steel handle that screws into the tripod socket. This grip lets you take the weight of the camera in your palm, freeing the fingers of your left hand for focusing. It also provides an opposing surface when you squeeze the trigger to advance, so the camera isn't pulled off-target. It even improves vertical shooting by letting you balance the camera on your palm. For anyone who wants to use a VI-T, I highly recommend it... and if you can't find it, the currently-available Voigtlander grip might be a good substitute.
Having defended the VI-T as the quick, facile shooter it is, I still have to say that most people are going to be more comfortable with a 7s. One big reason is the viewfinder: the VI-T has
reflected parallax-compensated framelines for 50mm and 100mm lenses
only, plus a separate unframed position for a 35mm lens. The finder image is 1:1, which is nice, and the extra magnified "Mg" position is handy for accurate focusing of long lenses.
But the reflected frames still aren't nearly as clear as the 7s's
projected frames, and the 7s also has a wider range of them: 35, 50, 85, 100, and 135, all parallax-compensated and all neatly labeled in the finder.
Other than the finder and the winding mechanism, the two cameras are quite similar feature-wise -- same stainless-steel-curtain shutter, same type of shutter speed dial, etc. The 7s has a CdS meter, which is handy if it's working but probably not quite handy enough to be your only meter; the same is true of the accessory clip-on meter available for the VI-T. The VI-T has that crazy little pin in the accessory shoe that provides automatic parallax compensation for V-series accessory finders... but the 7s's extra complement of framelines means you're less likely to need accessory finders in the first place.
So I'd say that for most people, the 7s gets the nod for its more familiar thumb wind, and its superior and more versatile finder. Oh, yeah, it also has the external breech-lock flange you'll need if you ever get the urge to try the 50mm f/0.95 lens (and if you do get the urge, you'd better do it quickly before all of them get cobbled into Leica M mounts!)
Incidentally, if you found a 7s for the same asking price as a comparable VI-T, you're doing a great job of shopping! VI-T prices have always struck me as inexplicably low... sure, the finder is a bit quirky and the trigger wind isn't to everyone's taste, but it's still a beautifully finished, low-production (about 8,000) camera that represents the last of Canon's trigger-wind era, and you'd think that would make them worth something, but prices seem to have been in the doldrums for years while other Canons such as the 7s and the P have gone up. I guess people who haven't tried it just really hate that trigger wind!
Gratuitous camera p0rn: