the CR is a two stroke, and the CRF is a four stroke.
There is absolutlery nothing wrong with a good 2 stroke bike. i ride one over a 4 stroke. they are less maitence, easier to fix, and really a blast to ride.
a used four stroke can be a ticking time bomb, a new top end on a 2 stroke is 200 bucks and some labor yourself, a 4 stroke top end is at least 1000 bucks with labor.
2 strokes are good first bike for everyone in my opinion.