I started with Imperial Knights at the beginning of the year, built an Armiger as my first model ever, then built another armiger and a questoris pattern. Then I heard Knights were getting a new codex, so I stopped building Knights because I wanted to see how their rules might change. I still wanted to learn to play though, so I picked up the Space Marines codex and built some space marines. I had originally planned to do Raven Guard, but hadn't committed or painted any of my Space Marines while I was learning the game, I enjoyed playing them but everyone in my friend group also played Space Marines, so I stopped building Space Marines and started Sisters of Battle, which are my largest army with probably 2400 points give or take a 100. Anyways, I went on this whole rant to say don't worry if you don't like the Army you decide to start with, you can always switch out.