I have all 3 of these, and did some comparison tests using a dummy load (3ohm (2amp @ 6volts), and 2ohm (3amps at 6volts)), measuring the voltage, and current of each test.

Obviously, the less the voltage drops, the more load there is on the BEC, so the comparisons aren't entirely accurate, but I believe they're fair none the less.

HXT UBEC 5/6v output, 5.5~23v Input
http://www.hobbycity.com/hobbycity/s...idProduct=3735
6.5v unloaded
6.0v with 3ohm load (2amp) = 7.7% drop
5.8v with 2ohm load (3amp) = 10.8% drop

TURNIGY 3A UBEC w/ Noise Reduction
http://www.hobbycity.com/hobbycity/s...idProduct=4319
6.0v unloaded
5.7v with 3ohm load = 5% drop
5.5v with 2ohm load = 8.3% drop

Turnigy 5A (8-26v) SBEC for Lipo (falsely advertised, this is actually 3amp also)
http://www.hobbycity.com/hobbycity/s...dProduct=10312
5.9v unloaded
5.5v with 3ohm load = 6.8% drop
5.3v with 2ohm load = 10.2% drop

So, in my opinion, if you want to maintain the highest possible voltage, go with the Hextronic, if you want the least variation in voltage, then the Turnigy 3amp seems like the better choice.

Hope this helps someone out!