My favorites and reasons:

I am going to like the Selesnya guild first because I like the creature-based play style most. However I might end up choosing to play Chavest (Rakdos + W) Tokens or Esper (Azorius + B) Tokens due to the support that still exists in Standard. Both follow the same strategy with their own spin on it.

My 2nd favorite guild will be Golgari as I do like a good zombie deck. Once again though my build is a 3-color Jund build featuring Dreadbore and Falkenrath Aristocrat among other things.

I'm still having issues deciding what I like most. My gut tells me Golgari, just because I've always loved the G/B combo.

I also really want to make Azorius Flicker Detain work. Azorius Justiciar/Lyev Skyknight/etc. + Restoration Angel/Cloudshift/Ghostly Flicker/etc.

And Izzet is just begging me to try and break it in some way..... Especially because I love the Overload mechanic.

I think everybody is underestimating Rakdos too much, so I also really want to build that for some crazy aggro.

So yeah, I'm torn and can't really pick a favorite.......

I'm going with Azorius because of curve of flyers available and the control it offers. Hopefully, it'll play well against Izzet and Rakdos... Golgari's Troll looks scary to face too... A turn 3 attack for up to 7 damage + regenerate and trample is crazy. Especially when you can start scavenging what you discarded as well. :-)

In two days of pre-release I'm playing Golgari and Izzet.

Personally, black and green have always been colors I've enjoyed and the combos that come out of Corpsejack Menace are just ridiculous. I'm going with Izzet on day two simply because I'm hoping to get more pieces for a deck that I can use the 2x Talrand, Sky Summoner I've been sitting on for a while.

I officially signed up tonight. Went with Azorius.

Literally, almost everybody is going with Golgari or Rakdos at my LGS, and a few for Izzet.
Selesnya was entirely blank. Nobody. At first I went with Selesnya, just to get somebody to play it and go against the grain, but I changed my mind later on in the night.