Voted Sandisk.
Sandisk has not failed me.. and their cards are fast and reliable.
I WILL NOT buy Lexar.... Recently I got a Platinum II 8gb card.. the pin separators broke off very quickly.. then recently a corner broke off while inserting into the camera. This exposed the electronics inside and killed the card. When i talked to Lexar Support online, they told me they cannot help me, and there is no local service centre, so if anything I'd have to pay to send to USA for checking even though they claim there is a lifetime warranty.
In short, don't buy it. Whatever lifetime warranty they claim is useless... they claim there is no warranty for breakage even though the warranty clause states that they cover "defects in workmanship and materials" and this is a clear cut case of defects. Even if you suffer data loss, sending it to USA for service would cost about as much as getting a new card.
QX