If those are the only two choices - I'd go with Colette. Reason - she does her own cakes. Martha has Kate Sullivan and others doing them for her.
Theresa 
2 different mediums...but i would choose Martha because her style is simple but elegant
Love love love love Collette I wish she were my fairy cakemother!
Love love love love Collette
I wish she were my fairy cakemother!
Me too!!!
While both are talented, Colette is a true artist. Her cakes stretch the bounds of imagination. I wish that she was my fairy cakemother, too!
There's no comparison because they are not both cake decorators. And if Martha is to be judged on her cake deco skills then she's no where near the same stratosphere as Colette.
I agree with what's been said above........but an interesting aside might be that if you're referencing many of the cakes you've seen in MS Weddings, they were actually done by Wendy Kromer, now of Sandusky, OH, but at one time, out of NY and a personal friend and, if memory serves me right, an intern and/or assistant to Colette.
Rae
Yes, (as Blakescakes said) the cakes in Martha Stewart's Wedding Cake book are all done by Wendy Kromer (as are most of the cakes in the magazines) We stop by her bakery in Sandusky every time we are up that direction! LOVE her work!!
Now, if you are comparing Wendy and Colette, that would be a tough call there. Wendy is the reason I started making IMBC - my DH tasted it for the first time at her bakery and insisted I make it here!
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