Conversation and sectional sets are the largest outdoor purchase most people make, and the one where the listing photo tells you least. What decides how a set looks in year three is the frame material, whether the cushions can be replaced, and how the pieces are joined.
Aluminum cannot rust and HDPE cannot rot, so both are low-worry anywhere. Powder-coated steel is strong and cheap but rusts from the moment the coating chips. Resin wicker is really two materials (a woven polyethylene shell over a hidden metal frame), so check what the frame underneath is, because a steel frame can rust from inside the weave where you cannot see or treat it.
This is the single most useful question to ask before buying: does the maker sell replacement cushions? A set whose covers can be replaced has a much longer real service life than an identical set whose covers cannot, whatever either listing claims about weather resistance.
Sectionals sold as separate seats and corners can be rearranged for a different patio later; a single welded run cannot. If you rent, or expect to move the furniture seasonally, that flexibility is worth more than it looks on day one.
Light aluminum tube furniture blows over in wind. Cast aluminum and HDPE are heavy enough to stay put, which matters more on an exposed deck than on a sheltered courtyard.
Read the material comparison before committing to a frame, and the weather-rating explainer before trusting any "all-weather" claim on the listing.
More depth: how the five common materials fail and what weather ratings actually commit a seller to.
Count the people who sit outside on a normal evening, not the largest party you have ever hosted. Most households over-buy seating and then lose the deck space they wanted. A four-seat conversation set suits daily use for a couple or small family; larger sectionals earn their footprint only if you genuinely entertain.
A conversation set is separate chairs around a low table, which is easier to rearrange and to move for cleaning. A sectional gives more usable seating in the same footprint and reads as a single piece of furniture, but is heavier and harder to reconfigure. Choose by how fixed your layout is.
Frames in aluminum or HDPE do not. Cushions usually do, unless they are explicitly described as fully weatherproof with quick-dry foam. In freeze-thaw climates a cover also keeps water out of seams and tube ends, where it expands when it freezes.