I have used RM at both DLR and WDW as well as UG at WDW. Here is why I like RM better:
1. RM lets you select your own rides as opposed to UG which selects them for you (broken down into categories of "teens", "families with small children", etc.) With RM you just put in what you want.
2. RM lets you add a ride more than once while UG assumes you only want to go on each ride once.
3. RM lets you start and end your itinerary at any time of day. This is especially valuable at DLR because of the ease of parkhopping between DL and DCA. UG assumes you will be at a park when it opens and that you will stay there all day.
4. RM is updated regularly online while the UG (for DLR) is a static plan from a book. Hence with RM you will know if rides are down for refurb while UG will not not that in its book.
My experience with RM at DLR and WDW is that the itineraries do work and are often a bit conservative in that the wait times in reality are not as long as what they predict. This gives yiu some added padding to your schedule.
The WDW version of UG does have an online version with more up-to-date plans and even has an itinerary planner sort of like RM but not as flexible.