The task of choosing our wedding party has been more difficult then I anticipated. There's also all sorts of baggage associated with it (as we all know I'm sure). This post at A $10,000 Wedding really sort of got me going on this topic.
At my friend's wedding last summer, of which most of the helpers were theater folk, we kept joking about the wedding as if it were a production.
"Two hours to curtain!"
"So, which songs do you want for the pre-show music?"
And while we were joking about it, I think that it is a valid comparison. You have the cast: Bride & Groom, parents of the couple, officiant, attendants, MC etc. You have a Stage Manger: Wedding planner/Day of Coordinator (whether you pay someone or not, or if it is even the bride doing this, you have someone...) There is tech help: Ushers, sound guy, DJ, some times lighting help, and of course your costumers, make up artists, set builders/designers, props etc.
To follow the metaphor even further, when you are casting people for a show, or choosing your tech crew, you consider their talent for the position (do you love them/ like them, want them to stand up next to you or are the creative/talented/artistic/organized) but you also think about their professionalism. You would never hire someone in a vital position if you couldn't trust them to show up on time and do their job responsibly, to take direction from those in charge, and to work well with others. So why would you ask someone to work on your wedding if you can't trust them to do the same thing?
I have seen, in friends weddings, a situation where a bridesmaid was chosen because she was like a sister to the bride, even though the bride has a history with the girl of her being flaky and/or selfish as well as committing to things, and then dropping them later when it became 'too much'. She picked her because she loved her, and just hoped that the lack of professionalism wouldn't come into play. Sure enough, not long after the planning started in earnest, this girl was problematic, and causing stress for the bride. In the end, we were all scrambling to make up for the responsibilities that the bridesmaid hadn't done, the morning of the wedding. Retrospectively, the bride may have chosen to give this close friend a different role, where less was at stake, perhaps greeting guests, manning the guest book, helping to set up day of etc.
My point? Choose people to stand with you that you love and want to be with you on your wedding day, but also consider their level of professionalism, because if you wouldn't hire them to do the job, you shouldn't ask them to be part of your wedding party.