Not many artists design their work with the idea that someone is going to put their lips on the work.
In the design of my cups this is exactly one of the things I consider. In addition to how the cup feels against my lips, I also think about how the cup feels in my hand if it is balanced. Of course the visual stimuli: color and shape are just as important.
In most of my cups, I like the rim to come to an outward taper. I feel like with this shape the rim conforms to my lip, almost as if the cup comes to meet my lips. I like that, but it does feel different the first time you drink from a cup designed like this.
I like the feel of a thin rim as compared to a fat one. However as the rim becomes thinner it also becomes more fragle. The rim is one of the most likely places for a cup to chip.
Esthetically, I like a rim that goes straight up. So I make both kinds of rims.
One thing I think about when making the handle is how I expect the handle to be gripped: with one finger through the handle, two fingers, or several. I look to see how the handle fits to the cup. I think about the negative space within the handle and how that fits to the shape of the cup. I have several types of handles to meet the preference of the customer.
I was reading what a judge had written about handles one time. She said that round handles are only found only on the cheapest of cups. The next article was from an established potter on how he decorates his cups, all his handles are round.
This is another place where the esthetics and the feel are different for me. I often think a round handle looks better on a cup, but I do like the feel of a flat handle. I have better control over the cup with a flat handle.
Many potters have made similar comments about cups as I have here. I think one of the best reviews is in a video done by Pete Pinnel.