Funny, I had this very same conversation with Andair at the show.
Assuming that you used an aircraft quality hose, either would be technically acceptable. Now on the practical side, in a small area -6 flex line isn't so flexible and with end fittings will be bulky in an already tight area. I just remade my lines from the fuselage fittings to the valve using the 3003 aluminum tube as I didn't like the way the original builder had done them. Not my favorite choice of alloys, but these lines only see static pressure and the soft tubing lends to tweaking the bends for final fit much better. A tubing bender is highly recommended if not required to prevent kinking the line.
The other option would be transitioning hard lines to flex at some point adding fittings and a union to the mix, again in tight areas.
I am going with the Andair valve as a replacement and think the tubing route will be what I will do.
RV6 built and sold
N199EC RV6A flying
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