What opening move (for white) should a beginner specialize in?

So I know that a beginner should focus on tactics and endgame study before learning openings, but that a beginner should also know the basics of openings. At the very least, I should study one opening move for White, one Black response to e4, and one Black response to d4.

The question is, what opening move for White should I study?

For e4, open (or semiopen) games are more direct and straightforward, but opposing players are booked up to hell on these games. 

For d4, it's not as straightforward as an open game, but IMO more interesting.

c4 seems a bit weird to me, but my (2200) friend swears by it.

The appeal of Nf3 is that I can memorize a set of moves and get to playing chess rather than booking up on the Ruy Lopez and Sicilian and whatever.

What move do you guys recommend I study?

I would recommend e4 simply because of what you stated, that it leads to games that are more direct and straightforward.  If you want a more interesting opening than the ruy lopez or sicilian defense I would recommend the vienna opening which is what I usually play.  The vienna is 1. e4 e5  2. Nc3.  There a lot of interesting variations that come out of that opening.  Also, if you wanted to try something with 1. d4 I'd recommend the Queen's gambit.

Just please don't memorize moves, no beginner should learn a opening name and the moves that must be played. Learning principles and the simples opening rules is all a chess player needs  until they get strong. The rules help you find the chess moves, might make a beginner play book moves even though he doesn't know it, but he understands his moves.

I do not suggest the English or Nf3, which is mostly the same thing. This is a very weird opening that is played from the flanks, where you can end up cramped in the centre. This is not intuitive at all and it also requires a certain technique. 

The d4-d5 openings often deal with minority attacks and isolani. Again, this is not so easy to play for beginners. If your opponent actually knows it a few moves you're lost for a plan anyway. 

I also don't like universal systems. That's the easy one way out. You will only ever learn to play one position unless you take up something else. 

Technically, any opening can be played if you play it like: e4/d3/Nf3/Nc3 or like d4/e3/Nc3/Nf3. So I'm going to assume you know a bit more than that. From that point on, the 1.e4 complex is more suitable and instructive.

Forget that you have to learn the Spanish or the Sicilian. You can play it with e4, bishop out, knights out, and d3. The 1.e4 opening is about white's spearhead e4 and the plan to press on with d4 or f4. The ideal centre is supported with c3-d4-e4 so black cannot take without loss of his only central pawn. 

Do not worry about the theory. Develop, castle and try to get the central majority. You can learn sharper lines later. The people you play are all in the same boat as you! 

I agree with Jempty.

I wonder if the beginner player is reading all this...

Beginner...Specialist?

Isn't that an oxymoron?

It depends how much time and ambition you have for chess.

• if your friend is a good friend and can teach you, then you can simply pick his openings and try to learn from him (you'll need lots of input from him though, as his opening choices are probably quite sophisticated, but the value of having an actual practitioner of the opening explain things to you is very high)
• if you're young and want to aim high, then 1.e4 and going for tactical open games is a good choice
• if you're less young, or don't have that much time, just pick anything you feel comfortable with

I believe going for tactical open games when playing with opponents on beginner level is more easily achieved with d4.  

To the op: Although, as I said earlier, I agree with Jempty, I believe that you still don't have to chose your opening to "specialize". As a beginner you should think more about tactics than strategy, more about attack than defense. I believe you would learn this best from gambits (with your opponent accepting them) as they teach you how to properly attack. I would especially recommend playing Danish Gambit Accepted as white (on chess.com you can start game from this position, not necessarely from standard one).

When you grasp the more advanced tactics, basic strategy, you can start learning the openings. Now it's too early.