I agree probably an active RC cut, if it's not Mexican tar cut with the usual- concentrated, brewed coffee (the residue from a burnt pot of coffee), brown sugar, etc...
I've had bth in the past that is equal to or subjectively better than ecp, I believe it's b/c I was one removed from the smuggler and there are other opioids besides heroin in bth, 6-MAM being one that many people like.
I prefer any dope that has a very slight odor of acetic anhydride (sp?), essentially a very slight vinegar odor. If it's too strong an odor I won't try it, that's usually spiked bth, as dealers know that knowledgeable dope users often check for coffee vs. vinegar odors, so they'll add a bit of vinegar to cover the coffee smell or sugar taste.
The best bth I've had either had no odor or that slight vinegar odor and was either powder (turns to tar with heat, hardens when frozen) or a translucent, brittle little rock. It always dissolved to a slight brown color, again translucent- could easily see through a loaded rig, and had very little undissolved residue or floaters in the rig. If your cotton is black it's cut up. If the cotton is light beige to light brown more likely less cut.
No guarantees ever though. I'm sure what I look for could be simulated and has been, but when you're only a few miles from the border (NOT San Diego, rather AZ or NM) or in MX you can get it uncut. But you gotta know the right people. I no longer do. Thankfully.
Bth can be excellent, or shit just like any dope but it's slightly more difficult to cut. Thankfully I kicked it years ago.