My primary system is my 3DS... as it was my first DS. I started playing at Gen V, and about a few years ago. Since then, I have worked backwards in acquiring other DS systems, as it is now my favorite gaming platform!
I also have a DSi XL, DS Lite, had a DSi but sold it on ebay... which I regret! If I had to choose a favorite, the DSi regular would be my favorite ergonomics and feature wise.
I often use my xl and lite for secondary playthroughs of Pokemon. So far I've made it through W1, B2, B1 next up W2!!