URs transfer to Marriott 1000:1000.
Transferring UR to Marriott is generally a BAD IDEA, except if you had a big stash of Marriott points already and you needed to "top off" that stash to make a redemption -- preferably for a 5 night stay to get one of those nights free and stretch the value of your redemption, or you knew you could get better than 1.5 cent per point value once your URs are Marriott points.
For a quick point of comparison, UR are worth 1.5 cpp with a CSR through the Chase travel portal, or 1.25 cpp with a CSP or CIP. Most people would peg the value of a Marriott point somewhere around 0.7 cent per point, maybe less with the upcoming category changes (i.e., devaluation).
As a real world example, Marriott recently announced that among the 1,600+ hotels increasing in category (therefore, points required per night) effective 3/4/20, the COURTYARD across from
Disneyland will be jumping from Category 6 to 7. A Category 7 hotel requires 60k Marriott points/night on a standard night, 50k/night off peak and 70k/night peak! The average cost for a room even on a busy weekend like 4th of July is only $359. This means if you were to use 60k-70k Marriott points on a room at this hotel, your Marriott points are worth barely 0.5 cents per point! Or you can book the cash rate at a fixed 1.5 cents per UR point through the Chase travel portal for 24k UR/night on your CSR.
Now, if you were to transfer UR to Marriott, you'd transfer 60k-70k URs to book one night. What a terrible value! You could book the same room, same night through Chase with your URs for only 24k UR/night.