Well both openings are playable, but the Queens Gambit, is actually better. Not only do chess theoratitions agree, it is just a common fact. In the kings gambit theking gets opened up way too much and black has dangerous tactics in mind. Even though the plans are stoppable, sometimes you will miss the trick and lose. That is inevitable, but in the Queens Gambit there are no tricky tactics like that, so the Queens Gambit. However the Queens Gambit is harder to learn, because there are millions of variations, and sometimes (almost always) the position gets extremely complex. So, in conclusion, the Kings Gambit is easier to learn and play, but the Queens Gambit, is theoretically (and actually) better, but more advanced. It is really a matter of style, but the Queens Gambit is just a tiny bit better. A very tiny bit, but that can make a huge difference.
Who decides the opening?
Some openings are called 'systems' (the Colle pops to mind) where you play a series of moves and end up in what should be a good position. Even these are trappish if you a sleeping at the wheel.
In checkers this question is simple to answer as they draw from a deck of cards to determine the openings..... in " 3 move restriction" which I understand is the most popular.....
I don't think any opening can be "forced" on the other player, because any given opening can be successfully avoided.
As white, I always open with 1.e4 (at least for now, cuz I'm nowhere near good enuf to be "bored" with it as I've heard some players say), and as black I always open with 1...Nf6 (The Dark Knight Opens 
). This means that I will never play a Dutch Game, Queen's Gambit, King's Gambit, and many other lines - from either side of the board.
Now since I am playing 1.e4, I must be prepared to face the Sicilian, the French, the Alekhine, the Scandinavian, or any of the other lines that come out of 1.e4. I could just as easily always avoid the Sicilian game by playing 1.d4 or something other than 1...c5 against 1.e4. If I'm black, and we play the moves: e4, e5, Nf3, Nc6 - I'm probably trying to steer towards (or at least anticipating) a Spanish Game. However, I will need to be prepared to face a Scotch or Italian game if that's what white ends up playing instead of 3.Bb5.
I see the openings like a sculpture. We start off with a new board like the sculptor starts off with a formless block of rock (or clay, or ice, or whatever other material he's sculpting from). First white knocks off a chunk of rock, and there goes all the openings that can no longer be reached (i.e. Queen's Pawn games if 1.e4, or King's Pawn games if 1.d4, or both if 1.b3, etc.). Then black knocks off another chunk of rock, and another set of openings is eliminated. Eventually, after both sides have whittled away at it, the resulting opening emerges.
So neither side chooses the opening, and both sides choose the opening. Eventually tho, they all turn into chess games. 
Archaic, yeah systems would break my description as a tree, i guess...come to think of it, long term strategic ideas are not as tree like as variations...and some are set up quite early in some openings, so maybe my original idea is not quite appropriate...
Adamperfection, I had not noticed that pattern, thank you.
Billium248, thank you as well, that is a very nice way to think of it :-)
dude chess.com is really hitting some homeruns today for lame threads.