This could get complicated. What sort of personality does your guild have, how large is it, and what's your budget?
For example, if it's a smaller guild that's mostly into applique, they probably wouldn't be interested in someone like Sally Collins and "Mastering Precision Piecing". (I have no idea if Sally does workshops, I just used her as an example.) On the other hand, they may be very interested in learning something new, such as precision piecing.
My dream wish-list of presenters include Yoko Saito, Cynthia England, Jamie Wallen, Margaret Solomon Gunn, Ricky Tims, Edyta Sitar, Bethanne Nemesh, Cathy Wiggins, Janet Fogg, Gena Perkes, Mark Lipinski (he's a hoot!).
There are several excellent suggestions upthread. May I suggest you look up the names, check pricing and availability, and put together a list of 5 possible speakers, then put that list to the guild for a vote? You could have them number the presenters in order of preference, the presenter with the most number 1 votes is the one you book. This may also give you presenters for the next 2-3 years.