Started playing IG 6 years ago, I've got about 3,500 pts. I chose IG because no one else in my area played them, but they remain my favorite army.
Started playing 'Nids 3 years ago, I've got about 1,500 pts. I started playing 'Nids because I wanted an CC army I could play sometimes instead of my shooty IG. I was torn between 'Nids and Orks, I wound up choosing 'Nids because I was hungry that day. No joke.
Started playing Orks about 2.5 years ago, I've got somewhere upwards of 4k. I started playing them because they are hilarious.
Started playing CSM about a year ago, because I wanted an army in power armor and refused to play standard marines. I've got about 1,250 pts.
Started playing SW when the new codex came out, not because I wanted to win games, but because they represented the Manly Marines better than standard marines. On a side note, the Manly Marines currently have a record of 4 wins, 1 draw, 2 losses. Technically I've got just under 500pts, the Manly Marines are a 2k list that currently relies heavily on proxies.
Started playing Necrons two or three months ago, because the monolith was cheaper than a land raider and they'll be quick to paint. Plus they're awesome.