im seriously considering going clipless, should i start with spd and move up to sl later on or just go straight to sl?

kinda starting to hate all the moving around my feet do in clip/straps, and i feel like my pedal stroke would be a lot cleaner and efficient with clipless
ive been paying attention to my knees a lot and i seem to have a good amount of knee tracking on my left side

is there any real benefit from one to the other or is it just mainly the shoes?
i like the fact that spd allows you to wear more normal shoes that i might not have to change, i like not carrying crap around