The interesting element tends to work around the guilds that players decide that they cannot play, rather than how guilds fit together. Typically most players seem to want to have a three-colour deck typically, sporting plenty of guild cards (which are typically stronger than their non-guild associates), but at the same time, especially in the Ravnica pack, there is good reason to hang back on picking gold cards, as they represent a very heavy colour commitment early on in a draft.
The big loser of full block draft seems to be Selesnya. As has been seen since the beginning of this Pro Tour, many have shied away from what used to be the default guild for a great many sealed decks when Ravnica block started - as committing to green and white strongly limits how one can jump into guilds in the other two packs. The interesting thing about this though, is that if one can somehow make drafting with Selesnya work, there are some gems as late picks all over the place. Over the course of the weekend there have been Glares and Hierarchs going later than one might expect, Evangels circulating fairly freely, and Watchwolf going as far as tenth. Drafting a strong Selesnya deck may require a little more planning than most (and crossing of digits for good Boros cards to go with in pack one, or good blue guilds in pack 3), but it seems the guild is open like never before.
Looking at the decks that have been winning their pods over the course of the weekend, there have been a variety of different combinations which have proven successful.
Top of that list is red/white/black. A traditional trio of guilds, in the sense that it only tries to fill up one guild at a time in each pack, this archetype can be either very aggressive, as was seen in Masashi Oiso's first draft deck of the weekend, using quick fliers, burn, creature enchantment pump and pushing the tempo, or very controlling, the style taken by Tomi Walamies' deck with Pillories, walls and pingers.
This deck gains some power by not having to fight for blue or green, which seem heavily drafted at the moment, but loses out a little in pack three, where it seems that everyone is happy to pick up a few quality removal spells at Rakdos' expense. This can mean rather slim pickings in pack three; which often need to be shored up by the quality mono-white cards in Dissension.
Taking Boros in a different direction is the red/white/blue deck. Many players feel that Azorius is the most powerful guild in the block, with its stellar fliers, great defense, and controlling style, and that Izzet doesn't fall far behind. With this in mind, being able to happily start drafting pack one with Azorius in mind down the stretch can be a powerful gambit. Neil Reeves in particular is a big advocate of the Azorius cause, and will typically be happy to splash black, red or both in the deck if appropriately powerful cards (along with the mana fixers for them) show up at the table. Between Soulsworn Jury and Azorius First-Wing, blue white has a whole new style of control now.
The other big archetype that has been very popular is red/green/blue. The astute ones among you might notice that this isn't a combination that includes any guilds from Ravnica, but at the same time it most definitely does include Simic, another top pick for most powerful guild in the block. Many of the Simic cards are at their absolute best when combined with Gruul, and the likes of Gruul Scrapper, who becomes a little nutty when combined with a graft monster or two.
While Ravnica can be a little bumpy for this archetype, there is a lot of potential to send good signals to others at the draft table in pack one here, and with two of the three Guildpact guilds helping out, there is a very good chance of catching the big hookup in pack two. For the final pack it should really be all about the Simic, who can be fiddly to get into for other archetypes, and big fat flyers along with lots of graft. For those of you unaware, Vigean Hydropon is very powerful in this deck, making all of your fairly efficient guys into complete monsters at the drop of a hat. Patagia Viper as Deranged Hermit that flies? Red/green/blue has the aggression and power to beat down, but also a little more control from its blue cards, making it very popular among the likes of Terry Soh and Justin Gary (each of whom were at the top tables at the start of Day Two).
It seems likely that as the format gets played more, there will be some shifting around with players settling into different archetypes as they see cards getting picked higher or lower. The important thing seems to be that whatever it is that you are doing, you have some sort of a plan going into the draft, and are aware of the wider colour implications of choosing a specific card or guild. The days of morphs and artifacts are gone; it's time to show your true colours as a drafter.