+1 on chain drive and not the cheapest...I did both, and was also dealing with craftsman. I think I got a step up from cheapest ($75 on sale IIRC) to lift a single door for a standard 2 car garage. Most of the attachment hardware between the door and chain/pulley system was a direct swap (my old model was an early 90s unit, so YMMV), but all I had to do was pop the new motor in the system, replace the chain and such and use the new systems sensors. Other than that, it was litteraly a motor swap
. No real measuring or anything too difficult. Reused the old rail and connectors to the door/ceiling etc. Was even able to use the same wires for the switch on the wall, so no new wires to run. All said and done, I think I spent ~2 hours including adjustments to lift force and travel adjustments. I really like craftsmans door openers, and will be a customer in that department again whenever the time comes. I would stick with them.
FWIW, make sure the door isnt LATCHED before trying to operate the door for the first time...I spent a solid half hour trying to figure out why when I clicked the remote, the door would move up a few inches, and then the whole thing looked like it was trying to implode into my garage...rails bending, gears grinding, metal squeaking. Im lucky my force was turned all the way down, or I coulda done some real damage.