I agree that car rental would be smarter for you. Two reasons; as was stated, taxi is going to run you about $35 - $40 each way (with tip), so car rental will normally be cheaper. But the main reason; some airlines do not allow you to check your luggage more than 3 hours prior to your flight. You'll need to check with your airline on their specific policies, but their information may make the decision for you.
45 Cruises & Counting! Favorites: Paul Gauguin to Tahiti: Uniworld River Cruises in Europe; any of the Celebrity Solstice-class ships; Holland America for 12-nights in the Baltics & Russia; RCCL for 14-night Greek Isles, Turkey, & Croatia; Holland America for 14-day Alaska cruisetour; 10-night Canada/New England cruise; 21 days in Hawaii including a 7-night NCL cruise; Oceania for 25 days in Asia; & 3 months touring Europe by train. And many days spent in all-inclusive resorts!