New 2TB portable drives formatted to Mac Journaled file system straight out of the box. Tested using Black Magic Design's Disk Speed Test with a Macbook Pro. Read and write speed was nearly identical for all drives except the internal drive.
The Seagate Backup Plus Slim drive is the winner on all dimensions: speed, price, size, weight though the Ultra is a little cheaper. The Silicon Power rugged armor disk is, well, pretty darn rugged!
The WD My Passport (old) line is a drive I have been using for about 9 months and is getting fairly full. I have not diagnosed whether the speed difference is because the file system/directory is getting full, or whether the new drives are about twice as fast.
I have the most experience with Western Digital Drives, and have never had one go bad over many years. I'm not sure how to assess longevity of these portable drives...I guess we'll have to wait and see.