I have always liked to use 8 and 10lbs test for spinning rod fishing depending on the fish species and the amount of cover in the water that you are fishing. If you can find it Yo-Zuri hybrid is one of the toughest lines on the market in my opinion been using it for lots of different fishing for many years now. It has a flurocarbon coatings which makes it work well around heavy cover and makes the line just tough.
I'm a Trilene man myself. I have three rods. Trilene line on all of them. I have 6lb, 8lb and 12lb test. I tend to use the 12lb if I am going for something big like lake trout, pike, catfish or surf casting at the beach. 35lb test line for ocean boat fishing.
What are you freshwater fishing for with 12lb line?