If you have an early morning breakfast for BEFORE the buses start running, an UBER or LYFT would be best. We used LYFT XL many times with zero issues.
If you are not in a time crunch, then boat to MK then bus to Riviera. If you are at EPCOT or HS for the day, then take the skyliner or bus.
We had breakfast at Chef Art Smith's homecoming @ 9:30am and too LYFT XL, Grand Floridian Cafe @ 7:30 am took LYFT XL, and since the buses were not at WL by 8:30am - we took a LYFT XL to HS to be there by 9am-and the line was still very long waiting for temp check/bag check. The buses in the morning at WL were not great.
Where did you get Lyft/Uber from DS?