The Enrollment Services schedule does not require a student account, is easier to navigate and gives more information about prerequisites and other enrollment restrictions but is not live data, and is only updated a couple of times a day. Use the Enrollment Services schedule to plan your schedule before enrollment opens up.
The schedule on UCONNECT is live data, and the schedule you'll use to actually enroll, but is harder to navigate.
The easiest way to create your schedule is to use two browser sessions, one for the Enrollment Services schedule, and one for UCONNECT. Use the Enrollment Services schedule to find the classes/CRNs quickly then switch to the Enroll, Add, or Drop form on the UCONNECT session to make sure the class is open and to actually enroll.