I carry both - primarily use my titanium card for in-person purchases, and the plastic AC card for any online/cardholder not present transactions.

Will fall back to the plastic version for certain machines that swallow the card as I've heard of the titanium card breaking them. Also had some issues where the titanium card has crashed the POS/card terminal, so have then used my plastic card.

Can't help with the ApplePay question - I'm based in the US, but iOS won't allow me to enter a non-US issued AmEx into the passbook app.