Options differ based on location - at my local airport Car2Go is notably more cost effective than Uber, about half the price. (You do have to shuttle to/from the parking, but I've taken it dozens of times without issue.) Limos (or limo company sedans, if you're solo) are also surprisingly affordable - they operate on a flat rate to/from the airport, which is only $10 more than a typical taxi ride from my house.