The most important consideration when choosing an outdoor recliner is finding one that will be sufficiently weatherproof. The chair will be outside exposed to the elements through all sorts of weather, and it will be at risk of sun damage, water damage, and dirt and grime, not to mention regular use. The outdoor recliner will therefore need to be well-constructed from high quality materials, and of course, it should be comfortable enough that you will want to sit in it regularly. Aesthetics are important as well, and you should choose an outdoor recliner that fits the aesthetic of the area in which it will be used regularly.
Synthetic materials are often used for constructing an outdoor recliner, and for good reason. Many synthetics are waterproof or water-resistant, meaning upholstery will not become waterlogged or water-damaged, and mold and mildew are less likely to build up on the fabric. Natural fiber materials can be used, but you will need to take care of the fabrics regularly and even store cushions indoors when not in use to prevent water damage. Above all, be sure the upholstery is comfortable and attractive, and make sure it is of a quality that will stand up to regular use.
The reclining function of the chair should be easy to use and it should allow you to recline into a comfortable position. Some chairs require you to push back on the seat back to engage the reclining function, while others use a rotating arm built into the side of the chair. Test out both outdoor recliner designs to see which one works best for you, and in either case, be sure the reclining function can be engaged and disengaged quickly and easily without too much excess effort. When reclined, be sure the reclining position is comfortable and stable; try shifting your weight while in that position to ensure the chair will not wobble or otherwise shift while in use.
Try to choose an outdoor recliner that is relatively lightweight. This may be more difficult than choosing a light folding chair, since recliners generally feature more material to allow for the reclining function, but many recliners are light enough to be moved around a patio area or stored easily. Be sure you can move the chair easily by yourself or with a partner. Some portable outdoor recliner models are made from lightweight aluminum and synthetic fibers, making them a good choice for trips to the beach or sitting out in the sun on the lawn, but they are not as comfortable as other types of recliners and certainly not as aesthetically pleasing.