let summary everything up:
T- the smallest in all, best if you like you carry your notebook around.
S - the second smallest but it was proven for quality over the last few versions
FS - with 15" screen and was introduced earlier this year, FS has suffered through many technical problems (monitor making noise, shor battery life...) BUT every changed after FS-6xx came out. The only problem left behind is short battery life (around 2hr15' right now which is acceptable) and sony is offering free upgrade to extended battery --> battery life will be apr 3h30 to 4h15 (don't look at the 5hrs stated by sony) ---> FS is one of the most kixk a** money notebook from sony right now.
A - this is the flagship, but remember one thing, it's freaken HEAVY and much much more expensive compared to any other noteboook. --> IMO, I rather spend money on some thing really cheap and then throw it away when Powerbook Intel Based is out.