I've always thought PTFE tape breaks down when in contact with oil therefore no good on a refrigeration system, so I got a tube of blue 'DiversiTech' sealer.
"Never use that stuff with R404a as it eats through it. Use PTFE."
I've seen it on flare nuts (that's a bit pointless methinks) and oil level sight glasses on scrollers and never seen a leak from one. The old school boys swear by it so I suppose they're right but I'd like to know what the masses reckon.