I like a lower and upper sub rail made with 2 x 4 stock..the rail cap is the same 2x6 decking.
I have also done some with Stainless tubing.
and some with vertical powder coated aluminum balusters.
Remember that railings must not be designed to be able to be climbed. That they are at least 32 inches or higher. And that there is a cross rail along the bottom so people with canes will not fall by pushing their cane out beyond the railing where there is no support for them to put cane on.
There are lots of great pre made types available all depends upon what you like and what will go with what ever it is that you have and where you want it installed.