Have rented from the airport Enterprise location on several occasions in the past. It is reasonably quick to pick up and return, nothing out of the ordinary time wise. The only issues with driving are the potholes, finding parking if you are in the city and the traffic. Make sure to have them mark all the damage on the car when you pick it up so you have no issues returning it.

My one bad experience driving in Panama: car in front of me slammed on their brakes to pick someone up standing on the side of the road, I stopped short, guy behind me rear ended me (no injuries, the bumper cover did pop off slightly though), I get out of the car to see damage, the guy who hit me pulls up beside me curses me out and drove off. Was able to pop bumper back in place and the bumper was in such a mess when I picked up the car that they didn't even notice the damage when I returned it (blessing in disguise I guess). This also happened within the first few hours of picking up the car which I had for 2 weeks. Again that was my only incident and again I've rented for long periods of time and on many occasions.

If you are only going to the canal I would say just take uber so you don't have to deal with it.