I read a ton of esc threads even though I just have one race worthy speedo right now (Tekin RS pro)
It looks like almost every manufacturer of the higher end speedos has just released or will be very shortly, firmware updates that will make them all pretty close to or maybe even slightly faster than a Tekin or Black Diamond.
If you can wait a little bit, it might become clearer if one speedo is truly faster than the rest (until the next batch of updates
). Right now I think the hobbywing xerun line might be the quickest with their latest 422 update, but then the Speed Passion update might make that even quicker. And Team Wave are on the cusp of releasing some firmware their team guys are raving about. Then Tekin might come out with new software to blow everyone away again. and on and on and on. If you need one right away I'm not sure what I would suggest.
Put all the names of the top ESCs on a dart board and throw.