Which external cross-over x-over to consider?

I would like to use an active x-over with balanced and single ended i/outputs between pre and power amps for a sub(Martin L. Depth) and my merlins, crossing over at around 40hz.
I never realized that there are a bunch of extrenal x-overs to choose from. Which ones would be of higher quality?
Here are some I have found, but I am sure there are many more:
Marchand's xm126 & xm-44,
nht's x1 & x2,
Bryston's 10b,
Mark levinson LNC,
deqx pdc-2.6,
Audio Research EC21.
If there are others worthy of looking at let's hear about them.