Here are the basics of wood flooring. If you want wood floors, you've got 3 main choices: 1.) solid hardwood, 2.) engineered wood, and 3.) laminate flooring.
Hardwood flooring comes either unfinished or prefinished. Unfinished hardwood tends to be a little cheaper than prefinished, but does require immediate light sanding, staining (optional), and sealing after installation. With prefinished, you can walk on it right after installation. With unfinished, you need to limit usage until it has been sealed. After sealing, you will need to wait at least 48 hours for the sealant to dry. Even then, additional coats may be required. With unfinished, the advantage is you can stain it and seal it to your exact specification. With prefinished, the advantage is the quick turnaround time.
One popular hardwood is bamboo flooring (a grass rather than a hardwood, nonetheless it's usually classed as a hardwood). Bamboo flooring is highly valued for its apparent "green" and environmentally-friendly qualities.
Hardwood must be nailed to a wooden sub-floor. Unlike the other wood flooring options, it cannot be installed straight on concrete or on top of your existing floor. Because of the nail-down requirement, it is recommended that you hire hardwood floor installers. If you wish, though, it is possible to rent floor staplers from home improvement centers.
Because hardwood is especially prone to scratches and dents, you will want to pay special attention to the Janka hardness rating scale and buy a species (i.e., oak, ash, etc.) of wood appropriate to your lifestyle and your budget.
Hardwood flooring's greatest advantage is that it can be re-sanded numerous times, extending its life literally for decades. Its greatest weakness: it cannot be installed in moist areas such as basements or bathrooms.
But it's the plywood that distinguishes engineered wood flooring from solid hardwood. Each ply runs perpendicular to its adjacent ply, giving dimensional strength to the sandwich. This means that engineered wood flooring stands up well to areas with light moisture--basements and bathrooms.
Another great thing about engineered wood is the range of installation options. The thinner varieties can be nailed down; the thicker kinds can be installed as floating floors. Floating floors are the great boon to do-it-yourselfers--no heavy staplers to lug around, no sub-floor. As long as your existing floor is level and stable, you can install the floating floor right on top.
Engineered wood flooring's greatest weakness is its thin top layer. Remarkably, this 1/16" to 1/8" finish layer can be sanded. But only once or twice. Three is pushing it. In any case, I strongly recommend you seek the advice of a reputable flooring company before sanding. Unlike solid hardwood, deep scratches and dents in engineered wood cannot be sanded out.
Rather, the reason it's included in this article about wood flooring is because it is an amazing simulation of wood. The resin layer is essentially a photograph of wood. You can examine it with a magnifying glass and still be fooled. The other reason it's included here is because most people buy laminate flooring as an alternative to wood flooring.
Among the advantages of laminate flooring are its scratch-resistence and the fact that it works well in topically moist environments like bathrooms and kitchens (unlike hardwood). And let's not forget: it's laughably easy to install.