Which opening for white pieces gave you the most success and/or rating points?

I've had the most success with 1.c4, but it took many attempts before I was able to "make it work."

Tried to play 1.c4 when I was 1500, was clueless. Tried again when mid 1800s, took me 3 months before I was equaling my 1.e4 results. 

Now it's my most successful opening move.

I play 1.e4. I like aggressive openings and open positions. I sort of learned from my grandfather's Morphy's Games of Chess and my style is influenced by his style, positional play and aggression.

I get good results with the Alapin Sicilian. Often Sicilian players do not defend well and I can push the center pawns. I also get good results with the Panov attack, often playing Qb3 after black plays Bf5 or Bb4.

I get good results with the Danish gambit at about 1800 level. If black knows the right ways to decline it, it is not good, but not that many of my opponents defend reasonably.

Within the last 6 months:

1. Ditched the Englund Gambit for the Grunfeld.

2. Switched over form d6 to e6 Sicilians to combat the anti-Sicilians club players 

3. Added the Reti to complement my English 

Mainly the Catalan for me. I like the Italian Game too.

Mostly random. But sometimes I was able to pull off 4 move checkmate

Damn it that server xD

Probably the Ruy Lopez, London, and Caro-Kann as White, and probably my Modern transpositional system (Modern, KID, Pirc, OID, Tiger Modern, various Indian Defenses), Ruy Lopez, Italian, Scotch, and Alekhine's as Black.
Granted, my Ruy Lopez was honed by playing it OTB like 10-15 times per week against someone who studied exclusively Ruy Lopez theory, my London success rate was purely due to nobody knowing how to play against it, and my Caro-Kann win rate was a gambit. I literally wouldn't recommend any of these (except maybe the London) to U1000 players, where I started playing them.
As for my Black opening repertoire, I'd fully recommend it to anyone of any rating with the addition of the Petrov for variety. 1... g6 against everything is a fully functional repertoire on its own, 1... Nf6 against everything also works (less flexibility but also less theory against e4), but 1... e5 against 1. e4 and then choose between 1... g6 or 1... Nf6 against 1. d4 is probably the safest and best repertoire.