Thirding the MSP option even though you're more likely to end up having trouble. If you end up late to MSP and miss your flight there will be a multitude of options that will get you into FRA only a few hours later than planned. If you are late into DTW from SLC you're basically assured of losing a day.

SLC has a lot of options as well, but you'd run the risk of something causing a delay after you'd boarded that caused you to be late to DTW. Better to have your short layover as early in the day as possible.