The Sandisk Cruzer, the Sandisk Ultra Fit and the Sandisk Extreme 3.0 are all reviewed highly as of 2015. The Wirecutter rates the Sandisk Extreme the best USB thumb drive.
The Wirecutter notes that there are other thumb drives less expensive than the Sandisk Extreme, but none come close to the performance. The publication tested read and write speeds. One drawback they note is the large size that may render neighboring USB drives on laptops unusable. Reviews of the Sandisk Ultrafit on Amazon.com like the small size, with it measuring only 3/4 inch long. One reviewer points out that the Ultrafit gets hot to the touch after only a few minutes. Sandisk says no function is lost as long as it is still within acceptable operating temperatures.