Huge difference to me for tipping is if it is a sit-down table service place vs. Over-the-counter fast food place.
Basically, If a human being comes and greets me, tells me about the specials, takes my order, brings me drinks and food, and the bill when I want it, that server gets a tip every time. Factors taking it up or down from my 15% nominal include: Timeliness/attentiveness of service, pleasantness/attitude, hotness if she’s a she; funniness/bro-ness if he’s a he, quality of food, quality of the establishment, and more recently I have added “if they seem to enjoy their job or not”. I find it uplifting and inspiring when people enjoy their chosen vocation, and that is becoming a bigger tip factor for me (waitresses & SP’s especially)!
I don’t run through numbers, just feel it through overall satisfaction level of the experience and tip accordingly.
However, if I order a coffee, a soda, an egg Mc-something and the server just has to grab it, turn around and hand it to me over the counter, then I’m like 0%, (or max 10% if somehow more pleasant than usual). This over-the-counter tipping with screens starting at 18% or 20% is a flagrant cash grab by the establishment imho, and I have decided to guiltlessly reject it. In fact, my buddies and I talk about it openly and agree, so we don’t feel cheap when we reject tipping for over the counter purchases. It would be like tipping the checkout lady at 7-11, and we are OK with not doing that, giving us more opportunity to tip bigger for propper service and incentivize service excellent moreso.
I do think some regs requiring a no-tip option on the main screen, and standard starting tip percentages would be helpful, especially for fast food and retail establishments.