First time from Michigan to Sierra Vista, az.. best route?

That time of year, I'd take I-65S to I-20W to I-10W. That will keep you out of the Appalachian Mountains. Even then I'd check weather reports for the major cities between (Wherever) Michigan and the Alabama border before you leave. Stick with the interstates until you're out of the snow belt.

If you're a Good Sam member, you can do a trip routing which is pretty helpful.

Which part of the route do you want to know about? Leaving Michigan? Approaching Sierra Vista? Crossing the country in between? You are asking about a long route across a part of the country with lots of choices.

At that time of the year you will deal with snow. It is more likely in Michigan and Indiana, but those states are also better equipped to deal with it.