Do Rhododendrons survive in Zone 5 in the UP of Michigan and which ones are the easiest to grow?
There is a partial list of those which growers have been successful with here:
Here is a link that might be useful: Proven performers
The University of Minnesota Extension has an excellent website on growing rhododendrons and azaleas. It lists a number of varieties that it recommends.
Azaleas and Rhododendrons for Minnesota
PJM is the hardiest rhododendron and is probably the first one to try.
The northern lights series of deciduous azaleas were developed for your climate.
Pay careful attention to the cultural requirements, most importantly good drainage and acidic soil.
Here is a link that might be useful: How to grow rhododendrons and azaleas.