As you can see in the chart below, UberSELECT pricing is also comfortably positioned between the other two offerings.
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The cars you can expect to see picking you up — the “BMW 3-Series, Audi A4 and Mercedes C-Class” for instance — are also considered to be middle-of-the-road. An UberX has cars like the Toyota Prius, while UberBLACK might pick you up in a Mercedes S-Class.