bunltd - 2:46 am on Feb 4, 2011 (gmt 0)
I've got dev licenses for Thesis, Genesis and Headway. They are similar SEO-wise, and I use them all for different reasons. (I've used woo and others for clients, fwiw)
Thesis is very flexible - so if you've got a specific look and feel you need to match or very specific functionality (custom) needs - it may make the most sense.
I like Genesis for the slick, good looking child themes - a bit of tweaking and you can have a nice looking site up and running fast.
Headway I've used where clients want to "do stuff" since it's got an interface they can fairly easily understand.
Woo isn't a favorite, some things they hard code (like dates) which should really be pulled from your wp settings. (although they have some nice looking themes)
my 2 cents. :-)