What is all your opinion on the best protein / musclebuilding substance to use for me?

I am 17 years old, 5'10 170 lbs. I am relatively strong, but looking to increase strength a little more but more of toning muscles etc.

Im not looking to become like super buff, just a more defined build.

Preferable something that is somewhat low-calorie, not too expensive that i can get from GNC or something

At your age, you can get some protein or maybe dabble in some creatine after you do a good deal of research on it and stuff.

yeah im looking at some ON whey protein

Honestly, I would avoid GNC if you can. Most of their stuff is dramatically overpriced.

Whey is probably all you need (if anything) - a lot of food will help too. Bodybuilding.com tends to have the best prices, or you can try Costco for whey if you have one near you.