Is there a train that runs from the airport to the train station in the city center? Or is just easiest to hail a cab? We are hoping to stay at the Hotel Loggiato dei Serviti.
There is only bus service between airport and the train station.
Flat rate to all hotels in centre of Florence is 20 Euros. Considering that you are two, you will have bags, you may be tired etc etc. Take a cab.
There is a shuttle bus that runs often and is inexpensive, provided you have little luggage.
The city of Florence has the Volainbus from the airport to the SITA bus station. Stop #4 is the bus station. Stop #3 is the Station Galleria which is the front of the SMN train station according to the map on the following website. http://www.ataf.net/tp/navigator.aspx?lvid=195&id_mtram=530152&cart=_&sts=AEROPORTO VESPUCCI&eds=AUTOSTAZIONE SITA&sl=Volainbus&lvdr=Di&dt=1&cmd=3# For the cab, our cab ride 4 years ago was 25Eu. The 20Eu flat rate may be new. But, it worked great. It was a nice and comfortable entrance to Florence.
It is 20 euro flat but there is 1 euro a bag I think and there often is an extra - like time of day, day of week, if the taxi picked you up somewhere, etc. Actually had one guy take me last spring from home to the airport on the meter and it was only 16 euro, which was very nice of him. There are some tips and a link to the official rate card PDF here: http://www.florence-journal.com/florence/2011/09/taxis-in-florence.html