We’ve tried most stuff and here’s my thoughts:
Teak:
We bought this first about 12 years ago and spent about £2k on table and reclining chairs. Really solid but a pain to store and part of the table has warped. Some of the joints on the chairs became sloppy so I took the apart and epoxied them so now they’re spot on.
I gave it all a good clean two years ago using proper two part teak cleaner and they looked like new. The now spend most of the time in the barn and only get pulled out if we need extra seating.
Powder coated Aluminium (with fabric seat base and back:
We bought a table and 5 chairs for the other side of the house about 8 years ago. Light and easy to move around, all the chairs stack so it’s easy to store. Still in very good condition.
Plastic Rattan stuff: We got a set of sofas for the other house about 4 years ago and they’re still going strong. It’s our holiday house so they don’t get hammered but it’s probably not the most hard wearing of construction but looks cool. Pretty bulky to store but still pleased with them.
We have a cover but frankly it would be a pain to put on and I’ll guarantee it’s will blow away. We just put all the cushions inside in a bulk bag that cost £5 off ebay.
We’re lucky enough to be able to store everything inside over the winter so hopefully we should get a few extra years out of all our outdoor furniture.
Just don’t buy anything made of steel!