Allan,
I am currently have the same questions? My Application is mostly data logging/recording of temperaturs, pressures, voltages, etc. I find the MultiMedia Card is probably the simpliest and easiest option. Requires just a small footprint.

However, I would like to have the option in the future to uses same flash card for external code memory. The MultiMedia Card does not have those capablities.

Pricing is going to make my final. decision. I have not finished research that area yet.

Scott