The best way to travel from Stansted Airport to the Americana is to use one of the bus services
The Stansted Express train service to Liverpool Street may look quicker but you will still have to travel from Liverpool Street to Baker Street on the underground or take a bus or taxi from there so the time difference will be zero
On all of the services you need to buy a ticket from Stansted to Baker Street/Gloucester Place - single or return
Easybus sell tickets for National Express & Airport Bus Express - it is always worth checking the price offered by them because it will often be a lower cost than booking directly - BUT - take care because sometimes they are more expensive than booking direct. The tickets are valid for the services one hour before and one hour after your chosen time.
On the way into London you will be dropped off in Baker Street just in front of a pedestrian crossing, cross Baker Street there and follow the walking directions to the Americana.
The return journey departs from in front of the Allsop Arms pub in Gloucester Place - it is 200 meters from the Americana.
Americana by Train
The Stansted Express to Liverpool Street Station takes 46 minutes and there is a frequent service.
When you arrive at Liverpool Street station follow the signs to the Underground and go to the Circle, Metropolitan or Hammersmith & City Line platform where all of the train go to Baker Street.
If you get on a train that is going to Hammersmith; when you get to Baker Street you will get of the train on Platform 6. When you get to the top of the stairs from the platform DO NOT take the exit to your right. Cross over the bridge and follow the signs directing you to the Bakerloo and Juberlee Lines. When you have gone through the Exit gates look to the right and there are some stairs that will take you into the upper part of the station, DO NOT take the steps on the left that take you directly to the street.
If you get a Metropolitan Line train to Baker Street it will stop at Platform 2. If you do not want to climb all of the stair to the Baker Street (North) exit you can take the short flight of stairs down towards the Bakerloo and Jubilee Lines. When you get to the bottom of the stairs look to the left and you will see direction to an exit via an up esculator. This will take you directly to the Upper part of Baker Street Station.
When you get to the upper part of the station, where the entrance to the Bakerloo and Jubilee Line is, look for the exit sign-posted as BAKER STREET (North).