Choosing faucets is about ergonomics and comfort using them as well as quality and appearance. Personally, I don't understand the benefit of Touch2O, because I can easily turn on my faucet without using my hands (I move the lever with my arm or elbow), but some people like to add new tech. To me, it's just one more thing that can break. If at all possible where you live, actually go to a showroom and try them out - you might like a pull down sprayer better than a pull out sprayer, or you might want a separate sprayer. You might using like a thin single handle that has curved edges, or a larger handle that's squared off. You'll be using your faucet multiple times a day, so see how they fit in your hands.

With respect to brands, I'm a big Hansgrohe fan (not Grohe), and have their products in my kitchen and bath.

Thank you. In terms of size/function for prep sink vs main sink, is there anything I should bear in mind? TIA

Once you have touch 2o on one sink youll be annoyed the others dont have it. Get it on both, its not that much more expensive. Full size faucet for both if the reach of faucet works for smaller sink (probably will if bowl size is 19" might not if thats the cabinet size). Most (all?) of the deltas come in stainless finish.

"prep sink vs main sink"

I don't have a prep sink -- in fact, I don't know anyone who has two sinks in their kitchen and I'm not sure I see the benefit unless you've got a 500+ sq ft kitchen -- but I would say get a full size in each (full sized sink too).