It's important that you understand that all fake Christmas trees are not created equally. Although most artificial Christmas trees needles are composed of poly-vinyl, the levels of quality differ greatly. Pay attention to the length and softness of the needles and find a texture that you like. It's also a good idea to examine the branches.
If you plan on putting any kind of decorations on your tree, make sure that the wire in the branches can support it. Cheaper trees will have thinner branches that are likely to bend and break under significant weight.