What is the name of the phenomenon that would make me choose A over B because I was influenced by a trend?
Bandwagon effect: 


  The bandwagon effect is a phenomenon whereby the rate of uptake of beliefs, ideas, fads and trends increases the more that they have already been adopted by others. In other words, the bandwagon effect is characterized by the probability of individual adoption increasing with respect to the proportion who have already done so. As more people come to believe in something, others also "hop on the bandwagon" regardless of the underlying evidence.


And the reason why you were not completely happy with the other questions you found (mostly on social pressure) is that there's perhaps not a single source of "bias" for the bandwagon effect. Depending on the actual phenomenon studied, social pressure or information cascades make more sense as an explanation for a given instance of the bandwagon effect. At least with respect to SE voting patterns, probably the latter makes a bit more sense. The two causes are probably not mutually exclusive.