Not tried teflon which sound interesting but on FT discussions there is criticism of variable finish quality.
I use delrin, stainless steel, glass, acrylic, acrylic over stainless steel, acrylic over brass and stainless steel over glass.
Overall delrin are cooler but on the same tank my stainless steel tip is actually the coolest I think because I use it with a steel tank replacement tube so heat dissipates into the tank? Odd.
Another site to look at is Signature Tips in UK.