I did some simple search terms based on tag, date, and a few other filters. Some example terms:
[visualforce] is:question created:2016-09
[lightning] is:answer created:2015-01
Just looking at the two tags you singled out and comparing them to the system totals, here's the data from last September (when the first
[lightning] questions started appearing) through the end of last month:
Tag Total Questions Total Answers Total Accepted Answers/Question Accept %
all 19936 21528 7968 1.08 39.97%
visualforce 3950 4331 1677 1.10 42.46%
lightning 498 435 174 0.87 34.94%
[visualforce] questions are answered at a slightly higher frequency than questions in general, and are also slighlty more likely to have an accepted answer. In contrast,
[lightning] questions see notably fewer answers, and are also less likely to have an accepted answer.
Here are some charts from the beginning of last year:
As you can see,
[lightning] is gaining some ground, but
[visualforce] is actually holding fairly steady with a pretty flat trend line this year, and still more popular than at the start of 2015.