Other than knowing that you get the best results from a frequency counter by using a high quality crystal, like an oven crystal, I don't know too much about a frequency counters.
I notice that you can get old big name frequency counters, like HP 53XX series, for about $300 used.
On the other hand you can new cheap frequency counters like the Victor for as little as $100. Another cheap brand is the Instek GFC-8270H/8131H which new is about $350.
Have these new frequency counters made the older ones completely obsolete, or are the older ones good deals with features and quality the new ones don't have in the $300 price range?
Note that the new counters tend to be MUCH smaller than the old counters, so if they are "the same" I would prefer a smaller counter on size issues alone. However, if the older counter is a lot more accurate/stable, then I might be willing to put up with the large size.
Also, I notice that "high precision clock" fanatics, like those guys that count leap seconds and stuff like that seem to prefer the old counters, so that might say something.