If you are new to dungeons chances are you may come across people who will kick you once they find out, people who will leave because they have to teach you. I think this is a great disadvantage to the game, and a disservice to those who recently joined GW2.
The map shout function can fix the problems a,b,c because you can specifically mention what kind of run you would like. However, this also means you are spamming the chat channel in that area or in LA to get a party together. So with convenience and clarity, we cause commotion and map spam. In a place like LA tons fo things can be going on from chats about WvW and whats happening to random people talking about whatever, and then to those seeking groups or members. This all turns into one giant spam wall of text that really takes away from the game. It also removes spam from the /map screen, so in turn fixes problems with #2. This however leads people to grief players as this site is not owned or operated by Arenanet, and therefore much like the dragon timer website, can be taken advantage of. This third option is very limiting in the way that you have to tab out to use, and the posts often become filled before you can get the group you would like.
A better chat based, or list based LFG tool in game would remedy this, but that is an entirely different discussion. Guilds are a great place to find dungeon members. Hopefully the guild you are in is supportive and enjoys dungeon runs and for those who are new, they are willing to teach. This method is great but works in the opposite way of the other methods. Instead of random people joining up in the open world, now you have caused only select people in guilds to do dungeons together. This makes those few people less likely to help or join with other players outside of the guild. So we have all those things going on, and this is just the beginning of your journey through a dungeon. As you can see, these steps themselves are a journey almost worthy of a story in their own right. But again, we have much further to go, as we haven’t even found a group yet. Now the fun part. We have finally found a group and we know what we want to do. We take our full group and head to the dungeon and the time either directly before we enter, when we enter, or shortly after, becomes the make or break of our experience.