I do TTM--> Observation. It's a pretty easy way to rule out ich entirely. While it does stress some fish out, I think it's probably less stress than most medications. The only fish I've ever lost to TTM were fish that were in extremely poor shape upon arrival, generally large terminal male wrasses. IME, larger terminal male wrasses are not great shippers. I think they're probably more sensitive to ammonia than your average fish, but I'm not certain. Given wrasses also tend to be rather sensitive to copper, I lean towards TTM. Some of them are very shy about eating during TTM due to stress, but I've never had one starve to death.
I have a pretty large stock of chloroquine diphosphate on hand (I like to keep a very well stocked fish medicine cabinet: chloroquine, cupramine, ciprofloxacin, enrofloxacin, erythromycin, trimethoprim-sulfa, amoxicillin, augmentin, nitrofurazone, praziquantel, fenbendazole, levamisole, and metronidazole), but given all the reports I've heard about chloroquine killing wrasses very quickly, I'm disinclined towards its use. I might consider it in a dire emergency (velvet). I'm generally not a fan of formalin. I know it works, but I'm always a bit paranoid about toxic and carcinogenic chemicals, even though the risk to humans from so little exposure is miniscule.
For the next round of non-wrasses I QT, I'm contemplating just doing a lengthy observation in a cycled tank with chloroquine. The biggest downside I can see to this is that there is no hobbyist-accessible test I'm aware of for chloroquine. UV light breaks it down pretty rapidly, and I believe plain ole visible light does to at least some degree.