As Jeremy said, the Sonnet:
Barefeats.com says that the Sonnet Tempo Pro is faster than all others because it uses the Marvel chip instead of the more common SI chip.
Ed
http://www.sonnettech.com/product/temposataproexpress34.html
This from barefeats.com:
The Sonnet Tempo SATA Pro ExpressCard/34 is unique among SATA ExpressCards in that it is the only true SATA adapter. Other brands say "SATA" but are actually using USB protocols. The result is that the Sonnet Tempo Pro produces much higher transfer rates. For example, when we connected the OCZ Vertex SSD to various SATA ExpressCards, the Sonnet Tempo Pro was 55% faster reading and 103% faster writing compared to the fastest alternative SATA ExpressCard
