Polygon have published an article on how to pick the right World of Warcraft main for you which seems very apropo considering it's the main thing I'm thinking about in-game at the moment. I think my decision is more or less made, but I thought it might be fun to go through their headings and see what my current thoughts are:
Why pick a Main?
I like having one, honestly! I like to consolidate my play time, achievements and goals onto one character. I play a lot of WoW, but not enough that I can be splitting my efforts; especially not in the early days of a new expansion. Alts are for content lulls further down the line. I've got more level capped alts now than I've ever had before, but that's mainly due to putting in a lot of effort on my Legion main early on.
For Gilneas! For the Alliance! It has to be. The article calls the Alliance, "stable but boring" with "a relatively young and untested king". Firm but fair, I suppose.
Class fantasy, and, Pick a class, not a specialization
This is really important for me. While my guild, Waypoint is pointedly Not an RP Guild, it does stand on that threshold and occasionally write fanfic. Lots of the older Waypoint alumni have carefully considered head-canon backstories for their characters, myself included, and that all feeds into class fantasy for me. At one point I was strongly considering maining an orc warrior, just because it fit the story of an Orgrimmar native going off to war, blindly following the orders of his Warchief.
Picking -- or rather not picking -- a specialization is also important. I like to heal, and I like to not die while doing over-the-top pulls in world content, so the hybrid classes than have a healing and tanking spec are favourites of mine. Here's a hint: I'm likely going to be picking two of them for my BfA journey.
Ignore the numbers
The article talks about sticking with a class even if they're not flavour of the month, saying that Blizzard strives for overall class balance and you'll be happier if you take the rough with the smooth over time. I guess that's largely true, even if sometimes it feels like balance is a long time coming sometimes (or not at all, on occasion). This, I suppose ties into picking a class based on the feel and fantasy of it; rather than it's raw output. I agree with the article here, but I understand that for a lot of players being the latest and greatest is an important considering, and there's nothing wrong with wanting to melt faces.
As for personal numbers, I do like to have Skada in dungeon and LFR runs, but I'm not obsessed with throughput, honest! I don't play at a high enough level for the numbers to be a massive concern. Normal-mode raids (and the occasional heroic stomp once vastly overgeared) were the limit of my participation in Legion, and most of my raid time was in LFR. So I can get behind ignoring the numbers.
Pick your own talents
I'm on the fence about this one. I just got finished saying I'm super-casual and the numbers don't matter at my level of play, but on the other hand, I like to be optimised. I like to know I'm doing the best I can, given the content I'm running. So I often look at Wowhead or Icy Veins guides for my spec and pick talents based on their advice. I do, however, sometimes pick something sub-optimal if it's really cool looking. I couldn't give up A Murder of Crows when I playing my Survival Hunter, even though it's not the best choice in that row. It was just too much fun to use. So I suppose what I'll do, in pratice, is take the optimal build from a guide, and then apply my own Rule of Cool to it until I'm happy. That seems like a reasonable compromise.
...that's all Polygon have to say on the subject. I broadly agree, especially with picking a class vs. picking a spec. Most of the advice boils down to pick something you find fun and it's hard to argue with that. If you're making a choice based on external factors -- like knowing your guild requires a niche filling to compete in progression -- then you don't really need a fluff piece article from Polygon to tell you how to proceed.
As for my own class choices for BfA, I'll be making a post in the next week...