the first prebuilt coils I ever used were Kanthal and I had the same experience. Seemed like every juice had a metallic aftertaste. when I started making my own wire and building I got a deal on boatload of Ni80 so that's what I've been using. I see a bulk purchase of SS in my near futureIMHO ss has a better taste.
Once I switched to ss and then went back to a kanthal build it was like I could taste the wire.