If you can find a CZ6a or CZ-70 I would go with one of them first. The 6a is the analog version with knobs, salt switch and is water resistant ( not waterproof but I have hunted in downpours with mine and it worked perfectly). It does not have a speaker and you can find the 5 inch and 10.5 inch ( and possibly the elusive Sunray FZ-12 coil ) for it ( this goes for the CZ 5, 7, 7a and 70 I believe as well). I would stay away from the CZ6 only due to the different coil connector. But I believe I saw a near mint one in the classifieds that may be a good pick up. The CZ6 is basically the same as the 6a and 5, but like I said, I think it has a 4 pin connector where the others have 5 pin connectors ( I may be wrong on the 5 vs 4 ).
My main choice first would be the 6a, followed by the CZ 5, then CZ-70 and then the CZ-3D. I hear the 3D shines in older parks and older sites but has some problems in trashy, aluminum slaw areas. The only thing about the CZ-70 ( not sure about the 3D) is that the sensitivity adjustments are in increments due to it being digital and push pad menu. I like the 6a and 5 because of the knobs and you can fine tune the sensitivity.
I hip mount my 6a and use the 10.5 inch coil for beach hunting and farm field hunting, the 8 inch for all around use and the 5 inch coil for coin hunting in trashy areas. That 5 inch coil can sniff out silver dimes and jewelry like crazy.
If you do get a CZ, first and foremost...do NOT raise the sensitivity above 2 or 3 for the first 20-25 hours of use. And a slower sweep speed is the ticket with these machines. Sweep targets from multiple angles and if it rings high tone repeatedly from all angles....it's a coin. Whats really nice about the machine is if you only have an hour or so to beach hunt and only want to hunt for gold, you can dig only the mid tone targets. Use the discriminate setting of 0 and LISTEN to how the target is reacting. I use discrimination setting of 0 about 90% of the time unless there is so much small iron and nails that I don't want to listen to the low tone, then I move it to 1. Be aware that if you do hunt in discriminate of 1 or higher, you may get fooled by some iron because you do not hear the low tone. Also, it is written that CZ's do not lose much if any depth the higher the discrimination setting. I really cannot confirm that, but like I said, I don't go higher than 1 anyway.
The CZ's are really great machines and I won't ever give my 6a up. I have about 8 detectors and use all of them from time to time, from the programmable DFX to my X5, to my Tejon to my PI to my water machines ( all great machines by the way). The thing about my 6a is I never forget how to set it up. 15-20 seconds to ground balance and away I go. I know exactly what sensitivity I am at and what discrimination level and GB with a 2 second look at the machine....and it has 3 tone ID along with a wide scan all metal mode and pin point button for sizing targets
Sorry for being a little long winded but when I get a chance to praise my 6a I will !!
Also...check out this site....lots of CZ tips so you can read about them. I hope you get one soon and join the CZ club.
http://66.51.97.78/coinist/cztipspage1.html