I would usually approach these types of decisions by doing research in advance, so that the options can be considered when not driving over potholes and hungry.

For example, the day before going to a city, A and B could each look up yelp reviews of restaurants in the city, and each write down a first choice and a second choise of the restaurants they would most like to go to, given constraints (eg. close to their other destination, open at the right time.) Then they could compare lists, and discuss, and decide which restaurant to go to before even leaving for the destination.

My impression from reading the conversations is that A and B are relatively good at communicating. They have different styles of communicating and different preferences. Over time, A and B might get to know each other's preferences better and be able to predict how the other person will respond with more accuracy, and that may shorten the amount of time it takes. I'm not sure there is a shortcut to convergence. The problem may be more that you are discussing things when tired and hungry and doing other things such as driving. If you have such conversations while you are both feeling kind of crappy, it may take longer to sort things out than if you discuss when in better circumstances.