So I've recently started having success with topwater baits.

I've been throwing a Rebel POP R and recently purchased a Rebel CHUG R.

The baits look identical with the exception that the CHUG R is longer.

So really whats the difference other than the size...?

Also is there any difference when referring to a popper and chugger

the difference is in the mouths. The popper is a concave bowl shape and the chugger is more of a V shape. The popper "pops" by creating an air bubble in that concave bowl mouth when you jerk it forward. The chugger throws water out the sides of the mouth as it "chugs" along.

The names are used interchangeably now, both describing a topwater plug that "pops" and throws water as it is retrieved.