To be honest, this doesn't have to be a final decision. It's completely fair to join a guild and then decide that they are not a good fit for you. Just be honest and upfront if you decide to leave, maybe give "2 weeks notice."
I would say flip a coin and join whichever guild, without holding any reservations. Whichever one you end up with, you are learning about your own style and what you do and do not like. If you are happy, stay, and don't worry about the "what if." If you are not happy, now you have a basis you can use when looking for your next guild.
Assuming out of all the guilds these were the two I liked the both. I would ask Guild 1 if I can do a 2 week trial to experience their guild. During those 2 weeks I check out the guild and at the end decide if that guild is worthwhile or not.
For me progression takes a bit more precedent over being friends. They will still be your friends even if they are in your guild and you can still do stuff like scenarios, dungeons or challenge modes with them. The clearing of "some" of heroic ds is what would concern me. My old guild went 8/8 heroic and they sucked.
Easy peasy. Go with the friends guild... I stopped playing wow when all friends left. Their is no point in playing with randoms or a guild with strict policys about this and that.. Vanilla we cleared almost all content (not naxx though) and that with only people who knew people so that everyone in the fucking guild knew someone IRL.
In TBC the guild split in 2. Some who wanted more raiding and some (who bye then where starting to get families etc ) who wanted more casual play. I choose the casual playing and we did Karazan and HC dungeons for most part. We also helped the HC guild out as replacements in raids now and then.
So Wotlk launched. We cleared Naxx, and went like 8 bosses in ulduar or so. We cleared TOC and we went 11/12 in Icecrown..´Best gaming times ever..