Doon Express arrives at 0435 hrs at Hardiwar so the main drawback may be the hotel check in. Depending on what arrangement you may have,normally the hotel will charge either full day or atleast half day rent as they will have to hold a vacant room for you.
The good part about Upasana/Kumbha Express is that they arrive in the afternoon so hotel charges will not be a problem. You can rest peacefully during the night & hit the ground running the next morning.
My recommendation is Upasana/Kumbha Express over Doon.