Redoran stronghold has the most inhabitants, many of them know how to fight, but neo real guards. Telvanni stronghold has dwemer machines as guards.
If you wnat a real cool stronghold use "island stronghold retreat mod". Just download and follow the instructions in the readme on how to install and to use. If you are not sure ofcourse I will help you in doing this.
You get island stronghold retreat (=Rothril stronghold) from here
