The only brand of these that I have firsthand experience with is Traben, so I'll only comment on that...
All in all, they make some really really good instruments for a low cost. I've had one for about 6 or 7 years now and don't regret it one bit.
This thread was started this evening on the subject of Traben: Traben Basses
In case you're interested.
Good luck, and happy hunting!