Any suggestions on the best way to get from Malpensa airpot to the central train station to catch a train to Florence?
The train about 30 mins. Be sure to catch the train to Centrale station.
A bus goes from Malpensa airport to the big railroad train station in Milan. I went in a bus from that airport to that train station. Finding and boarding that bus at the Malpensa airport was quick and easy. Being in the bus was pleasant. When the bus stopped at the big train station, I quickly stepped out of the bus, and my bag (which had been in the baggage compartment in the bus) was waiting for me on the sidewalk. The buss stopped very near a door to the big train station, I walked in, turned to the right toward the windows at which train tickets are for sale.
The bus takes an hour or a bit more if traffic is bad. Don't know how the price compares.
The best transport method will depend on which Terminal you're arriving at. If you're arriving at Terminal 1, the Malpensa Express (train) to Milano Centrale will probably be the quickest method. Note that there are two destination stations, Milano Centrale and Milano Cadorna, so be sure to board the correct train. You can buy tickets at the airport station, but DON'T forget to validate them before boarding the train.
If you're arriving at Terminal 2 (via one of the budget airlines), it's easier to use the Malpensa Shuttle (Bus) to Milano Centrale. The trip will be about 50 minutes (subject to traffic), and you'll disembark at Piazza Luigi di Savoia on one side of the station. Walk up two levels to get to the tracks. You can buy tickets for the Shuttle from the driver. One other point to note is that the Shuttle also leaves from Terminal 1, so you can use the it from there as well.
Both train and bus now run from Malpensa to Milano Centrale, cost 10 euros, and run frequently. I choose the train, since it's slightly faster and less affected by traffic. In case of a train strike, or if you just happen to find the bus first, then you can choose the bus. I would not pre-book an advance-discount train ticket from Milan to Florence when you are dependent on flight arrival and transfer time; it costs about $65 to buy a regular, 2nd class ticket in the station for the next train leaving.