i would keep it simple since the main focus should be the appliqued center- so 9-patches or a variation of them would work well- a disappearing 9-patch or a jacob's ladder block (just happens to be one of my favorite blocks) , split 9-patch, ribbon blocks would also be nice- or pineapple blocks---now that i started to think about it i can think of dozens that would work- do you have a favorite block to make? the sky is the limit= just keep it simple to enhance the center. (irish chain, double irish chain, bow-tie, log cabin, lemoyne star, friendship star, ...)