They all seem to work well, the second generation TB2 docks have less quirks and run cooler. So it comes down to what are the best port layout for you and best fit of ports, i.e. do you need SATA or optical audio or charging ports. There are subtle differences, for example, if you like to drive powered speakers, The Startech TB2 dock is the only one, I think, that won't give you an anoying pop as you enter or exit sleep. There was a "complete list" thread here while ago.
Oh, you will need to shop around for best prices, provantage used to have killer deals on the startech docks. Those that come with TB cables may be a little more money than those without, but if you need a cable, they may be a better value.