When iFixit tore down the Macbook Airs, they confirmed the use of Toshiba’s Blade X-gale SSDs. However, a thread over at Mac Rumors lead to the outing of a second SSD in later releases of the Macbook Air.
In the graphic below you will see two models, TS128C & SM128C. The Toshiba shows a read and write of 209.8 and 175.6 respectively while the SM128C (presumed to be a Samsung SSD), outperforms the latter with a massive 261.1 and 209.6 read / write.
Unfortunately there is no way to pick or choose your choice of Macbook Air when making a purchase. You will have to settle with whatever Apple has at hand when shipping your order.
If you own a Macbook Air you can check the revision number within System Profiler by going to > About this Mac > More info > Serial-ATA > Select the SSD > Revision.
If you have a revision number of AXM09A1Q you are in luck and have the quicker Samsung SSDs. A revision number of CJAA0201 means you have the Toshiba SSDs.
(Via Anadtech)