Very nice question!
I would tend to say 'all three' based on what I've done so far. The visual part is extremely important, but it's tricky to rely on that alone, because it's very easy to miss subtle details which turn out to be vital to the technique. So some verbal input in a demonstration of the technique is necessary, in order to highlight the important parts. This was really brought home to me when I was living in Denmark for a year (with very little Danish) and training there - lacking the vocabulary I tried to rely on sight alone, but would invariably miss something important, and would have to ask my training partner or the sensei to explain further.
I'm told that I talk a little too much when I'm teaching techniques (in the jiu jitsu club here in Ottawa), so I guess there's an optimum balance to strike between the visual and the verbal.
The 'feel' of the technique comes into play as soon as one starts practising it with a partner. Two sides to that, I think - firstly, getting the basic movements in the right place at the right time, which is tricky unless you've got someone to try it on, and secondly, to adapt the details of the technique to the particular uke you're working with (especially in cases where there's a significant size difference).
(Actually, the same thing applies to ballroom dancing, which I've been doing for a while - the same combination of visual, verbal and 'feel' is necessary to learn a pattern, and the way it fits into the dance, properly.)