First let's take a look at the pros and cons of non-wood outdoor furniture. Plastic furniture, it can be fairly durable and really reasonable price wise, but when you think about regular use, sun, rain, lots of moving around. A plastic chair or tables are far more likely to bend, crack and break easier than any other outdoor furniture. And maybe it is no big deal since it was fairly cheap anyway, but how many 'fairly cheap' purchases will you make till you realize that you have spent the same money you would have if you bought quality with having to constantly replace the plastic chairs. Not to mention even the nicest plastic outdoor furniture is not nearly as attractive as other options.
Then there are metal and iron, a main issue with these are that they will rust very easily, especially if you have them sitting in the grass. Metal and iron will collect moisture and once rusting gets bad enough the furniture will start to deteriorate and fall apart. Not to mention the thought of a metal or iron chair just seems cold, don't you think.
Now there is wicker, I love wicker furniture!! But, I will say that I believe it is better used indoors, all those nooks and crannies, they can be a pain in the butt to clean inside your home, how on earth are you supposed to get all the dust and dirt particles built up outside out of them?? A bonus to resin wicker though is that it is weather proof, it is resistant to hot, cold, dry or moisture filled air, it does not rust or stain, and all this is great, but it will still be more difficult to clean than solid wood will be. And with all the cleaning we all have to do naturally I can say I don't have the extra time for that... I keep my wicker furniture for the indoors!
Now wood, hardwood is a very smart purchase for outdoor furniture, why? It is naturally weather proof, some insect proof, maintenance is nothing crazy, and not to mention hardwood is beautiful! Hardwoods like Ipe, Garapa and Tigerwood are known to last a very long time; they are rich in color, weather, insect, and scratch resistant. There are other commonly used woods for outdoor furniture from softwoods as well, such as cedar, pine and fir, they are less expensive than hardwoods are but are still solid woods. If you love the idea of having wooden outdoor furniture but don't have the money for hardwood or hope to build your own, softwood is a good wood to work with. But if you hope to have the type of furniture to last a lifetime and pass down generations, you are looking at hardwoods, especially Ipe!