I instantly knew I will play the legions as always I was a fan of steel armour and longswords however you have to remember that you're not going to be locked in a faction so if you like 2 that means more fun for you.
As much as I think the Chosen are super cool, I expect them to be the most popular faction. I don't really dig knights and I am totally down to be a viking axe wielder, so Warborn for me! They also have the bast banner
You're not locked to one faction so you can switch if you want, I know I'll be playing both. Probable not the Chosen because they seem like the most popular faction and there's bound to be katana cultists and weabos on that faction.
I chose a Knight because I respect their background and traits. For example I like Knights because they're into high standards of code and discipline, bravery and protection of the weak. All of which I tend to favour myself.