First things first, check the airports' websites to see at what concourses those flights typically arrive and depart from. I had approximately 40mins in MSP going from Northwest US to the Southeast, and the gates also felt like they were at polar opposites. I made it, but it was a journey. It might be the same case for RDU-west coast.

I would suggest ATL over MSP, and I'm a little surprised to see some of the arguments for MSP. If you have to change terminals in ATL, you'll definitely use the tram. But I feel like you'd actually do more walking in MSP if you're changing. There's a lot of moving walkways in MSP, but it seems like every time I'm there half of them are out of commission. I did see a tram for one of the concourses, but I'm not sure it was a Delta concourse. I've never used a tram for any of my Delta connections. And if you are traversing across MSP, you'll go through some bottlenecks which can be very annoying. The straight terminals of ATL are a lot easier to navigate than the clusterf*cked concourses of MSP.

If at all possible, take into account some of the other variables like weather, MQMs earned, and alternate routes if you miss the connection. I feel like there would be more flights in ATL vs MSP that could get you somewhere that could eventually get you to west coast.