PhD: Should I choose a topic out of a comfort zone?
Pick the ones who interest you to meet with.  Probably some function (topics I like, big names).  I.e. y= f(x,t).

Who you meet with is not going to make your final decision on what school to go to.  But for sure you need to meet with those who you think are seriously "in zone" for being your advisor.  You need that scoop.  I would even make a stink if you don't meet with a key guy (their time is limited but so is yours...you are only making on visit...have seen candidates get a breakfast or lunch meeting or at least meet with grad student representative).

In terms of what work you should do, I strongly recommend to do something you are confident in.  This stuff is hard enough so you need an edge.  Also make it something you are interested in.  This stuff is hard enough so you need some enjoyment.  See.  Multifactorial.  Not f(x) versus f(t) but f (both).  maximize, maximize.  but each variable needs to be above average.  Say above 7 on a 0 to 10 subjective.  Don't let a 10  on one allow a 5 on the other.