We have the Chicco NextFit too, and we like it. The only thing I'm not super-fond of is how much harder it is to tighten the harness straps than it was on the KeyFit infant seat, but every convertible carseat I've tried seemed difficult to tighten so I don't think you'll get much difference with another seat (though I've only tried a handful, so maybe I'm mistaken). Oh, btw, DS is almost 30 pounds. Still rear-facing.
Re: What kind of car seat is your 2-year old in?