I'll not mention the cloudiness issue other than to say my flexible tubing is still crystal clear after 2 years. I guess it varies depending on the manufacturer and the coolant you're using.
Before thinking about hardline, read up about how you fit it. It is a whole lot harder to fit than flexible tubing. With flex you guess the right length, cut it flush, screw in your fittings in, stick the tubing on and then tighten everything up. With hardline you have to be much more accurate with the measurements. Unless you use a lot of fittings to let you just use straight tubing you will also have to make all the bends with a heat gun and a bending insert.
If you're happy to make the effort, it looks a lot nicer than flexible tubing IMO, but it's a lot of work.