I have 2 sons, (26 & 22 at present). I went with get them mid-range tools and broad sets that can handle what life throws at them. If they were professional wrench turners or farmers who depend on tools to make a living, then maybe consider the top shelf brands.
A better question, perhaps, than what brand is "what tools does a 18 y/o need starting out?" Of course circumstances will dictate some of it. Both of mine could have inherited some nice original Craftsman tools from my dad, but they both have cut themselves off from grandparents over politics. Would you rather your son has a really nice, high-end plier of a set of 4 mid-range that handle different tasks?
As long as connections are standard, mixing brands is fine, too. Got the oldest a set of Dewalt tools with a box. The younger one was pretty envious that Christmas. Got some Kobalt for them, too at times. Neither are especially handy, but both have apartments with girlfriend, so they feel the need to handle 'guy stuff'.