I'm a wood floor kind of guy. Not that there's anything wrong with carpet. Well, except that your average carpet is a Stepford kind of material, fake cloth spun up out of unnatural petro-ingredients, made expressly to lie there on the floor, gathering allergy-aggravating dust, mold, and spores all day.
In our part of the world, when we talk about wood floors, we're generally talking about strip flooring. Strip flooring comes in thicknesses ranging from 5/16" to 5/8" and in widths up to about 2 1/4 inches.
Every now and then, you'll see plank flooring, which comes in the same thicknesses, but ranges in width from 3 inches to 8 inches.
Finally, there's parquet, which looks like wood tile. It comes in squares, which are made up of small pieces of strip or plank flooring.
With rare exceptions, oak is the wood of choice. It has a handsome grain pattern, it wears well, and it looks good finished. Other woods are available, including ash and maple. If you're willing to seek out a flooring recycler, you can find heart pine and chestnut flooring. Chestnut is an oak look-alike; it's hard to tell the two species apart if you look at them side by side. If you want to know what ash looks like, go to a sporting goods store. Baseball bats are made of ash. If you want to see maple, check the floors at a bowling alley.
Oak and ash come if four grades. At the low end, there's #1 and #2 Common, which manufacturers gently describe as "rustic" in appearance. If you ask me, there's no good reason to install common-grade flooring. Labor costs are about the same regardless of which grade you use, and labor accounts for more than half the cost of the job. You might as well use the good stuff.
The first upgrade from common grade is Select, which is almost clear, but has some knots and color variation. At the top of the heap is Clear grade, which has only minor imperfections. Either of these two is acceptable. Look at both, and decide what it'll take to make you happy.
Maple comes in three grades: First, Second, and Third.
Avoid Third grade. If Second looks good enough to you, use it. If you've just got to have First, choose that.
There are three types of cuts: plain-sawn, quarter-sawn, and rift-sawn. Most wood flooring is plain-sawn. You get plain-sawn wood by cutting slices out of a log, bottom-to-top. Think cake layers. You get quarter-sawn and rift-sawn wood by cutting from the outside of the log toward the center. Sort of like cutting slices out of an apple. Quarter-sawn and rift-sawn boards have closer grain. They look better than plain-sawn boards. They're also a little stronger. Of course, they cost more.
Wood flooring also comes in a fancy, engineered form. The exposed part is real wood, which is glued to a layered substrate (think plywood). Engineered flooring is dimensionally stable, and can even be used in damp locations (like below grade), where plain old wood might warp or cup.
You can buy any type of wood flooring pre-finished. The advantages of pre-finished flooring are: (1) The appearance is consistent. (2) You don't have to worry about the finish flaws inherent to site-finished floors, such as dust, hair, and drops of sweat.
Disadvantages are: (1) You can't get a custom stain color. You're stuck with whatever comes out of the box. (2) Factory finishes are generally urethane, and not everybody likes the appearance of urethane. (More on this below.)
If you want to finish the floor onsite (which, of course, you'd have to do if you were refurbishing existing floors), you stain the floor, then apply one of the following finishes:
(1) Oil-modified urethane. Easy to apply, dries quickly, and yellows with age. A competent do-it-yourselfer could work with this stuff.
(2) Moisture-cured urethane. Better durability and water resistance than the above. Available in yellowing and non-yellowing formulas. Hard to apply. Not a good choice for DIY work.
(3) Oil-based varnish. Quick-drying, durable, and non-yellowing. Also not a good choice for DIY.
(4) Water-based urethane. Very quick drying, not much odor. DIY is a possibility.
(5) Wax. You just rub on layers and layers of solvent-based wax (such as carnauba). Never use a water-based "wax."
My humble opinion: Urethane finishes look like plastic, because they are plastic. When - not if - urethane gets scratched, it peels, and there's no good way to touch it up. I don't like urethane finishes, and I wouldn't use urethane on anything.
I like oil-based varnish. To do the job right, you have to brush it on. Varnishing floors is tedious, tiresome work, best left to professionals. That said, I varnished all the oak floors in my house, by myself. Varnish scuffs, but it doesn't scratch. If you had to, you could touch up a damaged spot.
I also like waxed floors. The finish is muted, not shiny at all. It has an aged appearance. Eventually, you have to strip the wax by tediously rubbing on mineral spirits. It's miserable work. Good news: A wax finish is ultimately patchable. You just strip it and re-apply.