tygon and clearflex are both good, the price of each will probably be the determinant factor. if you're rich you can run clearflex/tygon throughout your whole system, but you can also get some cheap pvc tubing from the hardware shop to span long distances if you're running an external cooling box (that method saved me a good 20 bucks)
i'm not quite sure what you mean by metal spring type clamps or edward ng's plastic clamps - if you could post some pics or paste some links that'd be awesome
but with the metal ones, if you're referring to the wormdrive clamps that you screw to make tight, i'd highly recommend using those with 1/2" ID tubing because plastic ones (i've only tried a few different types) have never worked for me with my 1/2" ID clearflex (not enough strength, the tubing is too stiff.)
protecting the tubing from the metal clamps is a sensible idea, personally i don't do it but i don't see any harm in it. with 1/2" ID / 3/4" OD tubing, the tube wall is a good 1/8" (3mm) thick and i prefer tighting my clamps until they actually start to eat away some of the tubing, that way i know they've got a nice tight grip
if you don't want to mar your tubing though you can either put something in between the clamp and the tubing, or just refrain from tightening the clamp to the point of damage.