Piper was my first favorite. She had pretty good writing and is very animated. I liked her attitude and pushiness. But It got boring pretty quick.
When I stumbled upon the Railroad and met Deacon, he became an instant favorite. He has a sort of charm that is very alluring. Great attitude. Fun stories. Very relatable to the main character(if you have full affinity, you'll know what I mean). I enjoyed his frequent change of looks and his sarcastic remarks.
Then I met Curie. I enjoyed her company so much, that even after deciding my character was not going to have a romantic interest.. I couldn't resist her charm. She is so cute and very intelligent. Relatable to the main character(because she is pre-war), and relatable to myself(thirst for knowledge, especially biology). I have her running around in an armored white lab coat with energy weapons. <3
My only issue with companions is they tend to like to crouch in front of me when I am trying to line up a snipe shot. Since they are so close I don't see that they are right in front of me. Then I miss my shot and potentially alert those nearby. I have to continuously tell them to "go over there" and make them wait so that they don't "sneak" in front of me again.
*edit* Sidenote - I do really enjoy Nick V., Dogmeat, and Codsworth. But they never really became my favorite. Nick came really close to being a favorite.. I still enjoy his company. Dogmeat is okay, but he doesn't help my style of game play. Codsworth can be annoying and comments on EVERYTHING, look buddy, I can pick a lock or pick up junk if I want to, okay?
Never fond of Preston, I don't like BOS, Cait is a little too brash for my liking(a nice change, but I only like it in small doses), Strong doesn't like that I lockpick and he doesn't sneak... Hancock, McCready, and X6-88 have not yet become my companions. I play a SLOOOOW game. Explore a lot. I know where to find them, just haven't gotten around to them yet. =P