This type of post is a bit of a snoozer, UNTIL you have to purchase engineered hardwood floors. Only then will you be happy our crackpot team of researchers (okay, just me) did the work for you. Like most things, you have to decide what works best for you in terms of the look and function of your new flooring.
What exactly is engineered hardwood flooring? And why choose it?
This type of floor starts with a bottom core (a "substrate" if you're fancy) of pressed plywood or manufactured wood layers, and is then topped with a nicer wood veneer; this top "wear layer" is the part that's seen once installed. The invisible bottom layers make natural movement easier, which prevents buckling or warping when temps fluctuate. It also makes it more affordable. The top layer gives it the look and warmth of solid hardwood vs. the cheaper, plastic-y feel of laminate.
Here's a rundown of some of the terms and considerations you'll encounter when shopping around for engineered hardwood floors. There are TONS of options and brands out there these days; you have to find the one that has the combination of features you desire.
Finish: You can choose either pre-finished boards, or choose to finish them once they are installed. In addition to a clear protective coat, pre-finished boards come in all sorts of stain colors, with names like "harvest" and "smoked oak." With unfinished boards, you get the control of choosing the perfect shade. You also get the extra work.
Plank Lengths: Floor boards will come in a box, in varying lengths, ranging from about 49" to the dreaded little 12". There's no way to control what lengths you receive, so don't be fooled by the nice long floor sample. Some brands do give you the upgrade option of longer length boards, so be sure to ask. Otherwise, you can buy more than required and attempt to cull out the very short boards.
Plank Width: This is pretty straightforward. What width you choose just depends on what look you are going for.
1-strip, 2-strip, 3-strip: This refers to the number of grooves on a single wide board, giving the appearance of multiple planks. This makes the floor quicker to lay, but still has the visual effect of smaller width boards.
Wood Grade: Select or Quality grades will have less variation in the grain of the wood and fewer knots. Builder's or Value grades will have more. What you choose depends on how much you care.
Floating: This is an increasingly popular method of installation, where the boards "float" above the subfloor vs. being affixed. Floating floors are less prone to warping than the glue down method.
Click Lock: This refers to the method of joining the boards together as they are installed over the subfloor. Individual pieces literally lock together in a special tongue and groove system. This makes for easier (and faster) installation, which you should think about if you are doing it yourself, or paying someone by the hour. If it's not a click lock floor, boards might need to be glued to each other first as they are installed.
Underlayment: This is the soft layer, usually foam or plastic, that lies between floating (not glue or nail down) hardwood flooring and the subfloor. Spend a little more on a thicker pad, and you'll reduce noise considerably. Cork is the Ferrari of underlayments.
Glue Down: With this method, the boards are glued directly to the subfloor, most likely concrete. Note that the glue itself can be expensive, so make sure to factor that into your budget. It can also be toxic, so choose carefully and plan for ventilation during installation.
Nail /Staple Down: This is just what it sounds like. The floor boards are nailed down to the wood subfloor. It isn't recommended for your average DIYers.
Top Layer Thickness: Here we're talking about the thickness of the top wear layer of veneer, which ranges from .6mm to 6mm. Really this number is all about sanding. How many times can you refinish your floors before you hit the "engineered" part of the floor? Stick to top layers with a thickness of over 4mm if you want your floor to last a lifetime (or more).
Janka Scale: This refers to the hardness of each wood species. White Pine is one of the softest, and is easiest to damage. On the other end of the spectrum are more exotic hardwoods like Brazilian Walnut. Choose accordingly depending on expected foot traffic, and your tolerance for worn-looking floors.
It's said that engineered floors are greener due to the comparatively fewer trees used to produce them. However, adhesives used in cheaper manufacturing processes can produce higher formaldehyde emissions. Before you buy, ask about the companies' environmental ratings. Similarly, buy finishing and adhesive products with zero or low VOCs.