first try with this company exceeded my expectations. i made a mistake of not making an advance car rental reservation on my recent trip to guam. all car rentals sold out at guam airport so I took a taxi to hotel. taxi driver (lady) recommended i try SIXT. got into hotel's free wifi, googled sixT company; got their number, called, and was greeted by Ms. Nakara. she answered all my questions and sent a sales rep, Marlon, to pick me up from my hotel to process my car rental. they have no airport office. their tamuning office is located just right down from airport road; it's <5 min drive from airport.
they do provide airport pick-up/shuttle service btw; so you need to reserve your car in advance. agent will be at airport arrival section waiting for you. you can't miss them, staff/agent in orange SIXT shirts.
they will transport/shuttle you to their office for processing; they accept both debit and credit cards; customer processing time seems quite efficient, a plus for me.
the vehicle i got was a newer model and quite clean. the price is quite reasonable for such a vehicle class. the sales agent and i completed car inspection outside and i was on my way in no time.
you have the option to drop off your car at the airport public parking section. just make sure to place key and parking ticket in the glove compartment and your good to go; very convenient.
based on my brief experience, i do recommend this company and i will use this company in the future.