Are you thinking 1x12 or 2x12? If its just a 1x12, you'll be fine with any speaker. If you are going to use 2, and they aren't JBLs, it will still be manageable.
If you ever decide to put JBLs in a 2x12, it's going to be heavy, especially if you put in "E"s (E"s are a lot heavier than the "D" or "K").
A 2x12 HT type cab with 2 "E"s in there is going to weigh close to 80 pounds.
I've been playing with one "K" inside a 1x12, and I'm happy as a clam.