Very short version, the B3 sounds to some a little better, and is more durable, the B6 hides better. Neither is a MKE-2 or a DPA. Each has their plusses and minuses.
Countryman, for both models, are best known for their resistance to sweat damage, and price
point. They are, however, generally the worst sounding; not that they sound bad, but they don't sound as nice in general compared to MKE-2s, DPAs, or the new MKE-1. They're a little harder to color (although nowhere near as hard as the new Teflon coated MKE-1...please,
Sennheiser, a matte version, please????) than the other brands, a
bit pickier as far as what markers will stay colored, vs what fades quickly. (See some of my previous posts on rigging and coloring mics for brand recommendations, with the added caveat that since I wrote those, Copic brand has become really popular, although I haven't tested it with Countryman cable, as I don't use Countryman terribly often).
The other big downside to both Countryman mics, but especially the thinner cabled B6, is that as a general rule, Countryman's
strain relief and termination is pretty awful. If you buy them to bare
wire and terminate them yourself, that's one thing, but buying pre-terminated, they use miserably useless
shrink-tube strain relief, and also seem to strip things back a
bit too far inside, causing nasty shorting sounds when the aforementioned crummy
strain relief softens up. They also, at least as of last time I went through that routine with them, refused to acknowlege the problem and consider it a warranty repair.
That said, I've been working as a repair tech for a shop the last couple years, and all my other dealings with Countryman have been great...they've been really good about taking care of other issues (particularly their
Lectern gooseneck mics) under warranty when appropriate. I just have issue with how they handled my repairs when I had lots of lavs out on a major musical tour, but that was five years ago, perhaps things have changed. (I know, however, that the termination has NOT changed, as it was still the bane of my existence on E6s on a few recent shows I had to use them on.)
For completeness, the DPA 4060
line is generally considered the gold standard in tone, although it's also got a rep for sweating out the fastest. The MKE-2 is second in tone, but much more sweat-resistant, IF you use it without a cap. The caps tend to
trap sweat in these (on Countryman and DPA, however, caps are a necessity).
The MKE-1 seems so far to be a great compromise of sweat-resistance, durability, tone, and size, although since it's only so far available in the Teflon coated cable, it sucks to color! But I would not be surprised to see it catching on more and more;
sneak previews of them have been going out on Broadway shows with most of the major designers recently, and the
feedback I've heard has been great. There are a few on the show I'm currently working on (although I'm on loan to the lighting department as
deck elec for this short run), and the sound team seems pretty happy with them, save the coloring issue.
HTH,
Andy