Where are you planning to be while in UT? If Moab and anywhere closer to I-70, east on I-70 and you can choose either to head south at the Minturn Jct (24) or you can stay on I-70 and go up, over Vail Pass and at Copper Ski Resort. head south on 91. Either 24 or 91 back to 24 south will get you to Buena Vista. All of it is going to be a pretty scenic drive.
If you choose to get to Montrose and head east on 50, that is also a great drive, especially in the Blue Mesa Reservoir area. Don't forget to consider seeing the Black Canyon of the Gunninson N.P. if on Hwy 50.
As already mentioned, Monarch Pass is not that big of a deal and neither are the other passes if you choose the first paragraph routing I've mentioned. It really comes down to what area you are coming from and what your desires are to see.