baron,
i used both I2C and SPI.
I prefer to use SPI it is faster and you can adress very big EEPROMs.
And when you disable the SPI chip with the enable line it is in powerdown mode and the BUS in reset state.
I change all I/O pins in software (not with integrated modules).
You can interrupted SPI all times in process (to do some interrupts).
(on I2C i have some problems with interrupts...not on all chips!!!)

I decide to use the cheaper chip.!
Sascha