We've seen many of the cards in the new RTR and there's been a lot of complaining that one guild is too powerful and another isn't powerful enough when some have had more of their cards spoiler than others. I decided to do a break-down of the cards spoiled so far and what guild they are aligned with by their guild mark and mechanics.
Azorius 11:
Azorius Justiciar
Martial Law
Archon of the Triumvirate
Azorius Charm
Detention Sphere
Isperia, Supreme Judge
Lyev Skyknight
Supreme Verdict
Judge's Familiar
Azorius Guildgate
Hallowed Fountain
Izzet 13:
Cyclonic Rift
Mizzium Mortars
Street Spasm
Counterflux
Epic Experiment
Goblin Electromancer
Hypersonic Dragon
Izzet Charm
Nivix Guildmage
Niv Mizzet, Dracogenius
Nivmagus Elemental
Izzet Guildgate
Steam Vents
Golgari 13:
Deathbridge Goliath
Abrupt Decay
Corpsejack Menace
Dreg Mangler
Grisly Salvage
Jarad, Golgari Lich Lord
Jarad's Orders
Korozda Guildmage
Lotleth Troll
Sluiceway Scorpion
Slitherhead
Golgari Guildgate
Overgrown Tomb
Rakdos 14:
Dead Reveler
Grim Roustabout
Chaos Imps
Auger Spree
Carnival Hellsteed
Deadbore
Havoc Festival
Rakdos's Return
Rix Maadi Guildmage
Slaughter Games
Cryptborn Horror
Rakdos Shred-freak
Blood Crypt
Rakdos Guildgate
Selesnya 13:
Eyes in the Skies
Rootborn Defenses
Collective Blessing
Heroes Reunion
Loxodon Smiter
Selesnya Charm
Trostani, Selesnya's Voice
Wayfaring Temple
Dryad Militant
Growing Ranks
Grove of the Guardians
Selesnya Guildgate
Temple Garden
Below are the cards that aren't part of a specific guild but by its actions will most likely fit with the guild it's posted in
AzoriusIzzetGuttersnipe - damage on casting Instants and Sorceries is straight up Izzet's alley
Pyroconvergence - "
The Izzet are an equation that turns lunacy into explosions" - Leonos, Azorius ArbitersGolgariDeath's Presence - Autoscavenge with Golgari flavor text
Vraska the Unseen - Planeswalker that is lined up with the colors in Golgari and meets the 'death' portion of its requirements, making the tokens is 'almost' life.
RakdosSelesnyaSlime Molding - Make a nice token to Populate
Finally, below are the cards that don't appear to fit with any guild in the set or specifically mention having no guild affiliation like in the flavor text of Fencing Ace.
Angel of Serenity - almost seems to be Azorius but it's being so much broader than Detain really sets it aside in my mind
Fencing Ace - Flavor text alone places it here
Pricinct Captain - Though it generates tokens like Selesnya, the flavor text and clothing in the artwork suggests no guild affiliation
Faerie Imposter - Will function great with Azorius, but appears to have no other connection to the guilds
Jace, Architect of Thought - No surprise here, Planeswalkers have never been 'stamped' in the past, not even Koth the Hammer from Mirrodin
Skyline Predator - a fast flying beefcake, not much else
Sphinx of the Chimes - Info on RTR says that Sphinxs with the exception of Isperia have stayed unaffiliated
Syncopate - a new counterspell that doesn't have any aparent affiliation
Desecration Demon - Nice creature but seems to fit AVR more than RTR
Ogre Jailbreaker - Though he likes the Guildgates he doesn't care which
Necropolis Reagent - Swings the game on its own, but not really aligned to a guild
Pack Rat - Most Easily abused by Selesnya, but totally out of their colors
Underworld Connections - Aaaalmost fits Golgari in that you gain from your loss, but still seems a shakey connection.
Guild Fued - Anyone can come and fight, just clean up when you're done
Axebane Guardian - Neat card, but nothing special for the guilds
Gatekeeper Vine - Though he likes the Guildgates he doesn't care which
Wild Beastmaster - Neat flavor, but no guildness
Worldspine Wurm - Big beats with treats, no gold for guilds
Chromatic Lantern - I makes all colors for all colors combos
Transguild Promenade - Everyone can come and party for any colors
As more spoilers come out I will add them to the list where they best fit.
For this initial post it appears that the guilds have received about an equal amount of spoilers with Azorius a little on the lighter end of the scale with 11 cards to the 13-14 of each of the others.