What's your favorite opening and why?

I usually play the Queen's gambit as white and the Sicilian as black.

It seems like more people are comfortable defending 1.e4 openings and 1.d4 seems more interesting to me.  It also seems like players that accept the queen's gambit run into trouble quick.

Similarly, players that open with 1.e4 seem to expect 1.e5, even though 1.c5 is more common these days.

What do you think? What are your favorite openings and why?

Against d4 I like the slav, and I like taking the c pawn as early as possible (if it is possible)

I personally will pretty much always attempt Queens Gambit from the get-go. I like this because worst case I take the center and develop the Catalan! 

 I prefer to play with the Black pieces with a hyper-modern repertoire centering on the Pirc and King's Indian Defense. I prefer the faster pace of the Pirc Defense.

These openings are so theory heavy, for now I've settled for exclusively playing the Accelerated London System with the white pieces. At a later point I'd want to expand into the Bononi against Black's early c5 pushes against 1.d4. When I become insufferably bored of playing the repetitive London System, I aim to learn the Catalan because I'm already comfortable the fiancettoed King Bishop structures.

I tend to work fluidly between the Czech Pirc and the Elshad for both Black and White. Both tend to get more experienced players out of their book early in games. I have my own style as White using the Reti opening to move between the potential openings of: Elshad, Czech Pirc, London, Nimzo-Larsen, King's Indian attack or the White Lion. Based on opponents opening strategy.

I really like the Stafford because a lot of players will fall into one trap or another of its lines and good looking moves end up being blunders.

@DonsTheKnight A lot of buzz on YouTube chess channels recently about Stafford Gambits.

As white, I always play 1. e4 and shoot for an Italian. I'm just very comfortable with this opening, I know the theory, I know the ideas. I'm not in love with it, though. I do better in positional games, so I love playing against 1. d4, but I never actually play it. 

As black, I'll play the French against 1. e4. I'm not sure I'm in love with that either these days, I've been heavily gravitating toward the Sicilian, but still pick the French usually as a comfort pick. And against 1. d4, I'll play Nf6 and bully my opponent into transposing into QGD by faking a Nimzo.