I've owned them both. If I had to choose, I'd pick the Retrax.
The Retrax is easier to open, IMO. It's also nice that you can lock the Retrax, even though I've never actually done that.
Retrax also has the built in rail system for attaching racks and crossbars.
The only drawback to the Retrax is that the canister eats up some bed space, but it's rarely an issue.
I can't comment on water leakage, because I don't care if my truck bed gets water in it.
I currently have the Retrax on my truck, and we swapped the BAK cover to our F-150.
Here are pics of them with our new PRO-X crossbars:
https://www.kbvoodoo.com/ford-f150