Your gown will set the tone for the wedding as to how formal or how casual, how traditional or how trendy your day will be. When selecting dresses for your girls, keep this same tone and theme in mind for them.
Traditionally, the bride had full say and control over what dresses her bridal party would wear. She selected the style and colour and her choice was not debated. And for a more traditional or formal wedding, all bridesmaids usually wear the exact same dress. The "PROS" of tradition is that there is no arguing or debating among bridesmaids which means less drama to deal with... and in the end, all the girls have the same look. The "CONS" of tradition is that the bride may select a style (or colour) that really doesn't look good on all of her girls, leaving some feeling self-conscious and less-than-thrilled about an expense that she'll never wear again.
More recently however, the dynamics of bridesmaids styles have shifted somewhat, allowing the girls to have more input and say into the dresses that get selected. And there has also been a trend towards allowing the bridesmaids to choose a dress of their choice, within certain parameters set out by the bride. The "PROS" of being more flexible is that each girl can select a style that she feels secure and comfortable in, and they'll be happier about putting out money for a dress they will indeed wear again. The "CONS" of individual choice is that the girls may look totally uncoordinated and sometimes giving too much freedom can end up with a bridesmaid selecting a dress that the bride totally dislikes.
So, what is the best option for choosing your bridesmaids attire?
In my personal opinion... it all goes back to what the tone, feel or theme of your wedding will be. If it is very traditional and formal, then all the same dress (or at least all the same colour and length of dress by the same designer, but in different styles) is the best way to go. But if your wedding is more casual and informal, then giving your girls guidelines about the colour and length and letting them choose their own dresses might be a better idea.
Regardless of how you decide to attire your bridesmaids... just remember to be considerate of their body styles, personal styles and budget as you make your decision. Don't alienate a dear friend over a dress disagreement.
And don't forget:
on your wedding day
it is MORE important
that your BFF's are standing up with you as your maids
than what dress they are wearing!