This is going to be a compilation of guilds on US Set server that I have gauged in terms of new person friendliness and helpfulness.
The Epic Guard: Friendly people and ultra smooth T4 runs but ultimately NOT new people friendly. They don't bill themselves as much anyhow so its fine. End game guild. Slightly elitist.
Legacy: Great guild, friendly people, and been around for a while now. They have some vet players that have wide raid knowledge from T1-T3. But they also have a lot of new players. A very good "permanent" guild that'll be great for someone that just hit 80 and for people who are topping off their characters.
Social Rejects(was Acolytes): Its a toss up with this group. Again each guild has great people/teachers and some not so great. I would put these guys more toward end game guild although I've been on t1s they hosted... but even the commentary over vent over "T1 crap" suggested they are a bit elitist. If you're new new, I would avoid this guild.
The Walking Dead: Yes... very BIG guild. They used to be one of the most "elite" of the guilds until they lost many of their "elite" players to TEG. They do everything from T1 to T3, all their runs are smooth and people are friendly...they still seem to have trouble with W2 and Chatha especially...but W2 is probably harder then most of T3 if you have a lot of new people.
I have not seen them do T3 upper yet. Good new player guild up to mid level... you'll certainly have an army of guild mates to call upon if you join.
Obsidian Dragons: They are reasonably friendly and I have run a few T3's with them, overall I think this huildbis more tight knit.. at least that's the feeling I get from them. Good guild, but are they recruiting?
KUSH: This guild has some of the most fun and colorful people in the game. I join purely for the vent lols..its worth it alone.Although the raids themselves are relatively sub par (at least the PUGs). They run everything from T1-T3 and I think their main raids can do Thoth, although I have not been on one. Overall, a good new player friendly guild where the guild personalities are top notch. They have some vets that can be elitist especially to people who don't have basic understanding of the raids.
Shadowdancer: Wow, an ancient guild with the original guild leader still active. Excellent PUG raids (although I've been denied once because I told them I've never tanked Stinky...just to gauge reaction). Overall, a mix of everything. New people/vets, t1/t2/t3. Good quality "permanent" guild.
Prophets: I have to admit they've probably got some of the more "top" vet players...but they are all foreign. Most speak good English, some speak the Queen's English so it can be a bit daunting over game FX and a bad vent ping. They would be considered elitist and I've run with one PUG wherein there was an assumption that you should know what to do and when. If you're new, avoid. Overall, if you're more mid cap and want to do some 3.5 raids, join.