Engineered oak flooring certainly has come a far way from a decade or so ago, when it was made from cheap wood pulp, and covered in spar varnish. Here are some comparisons between engineered and solid oak flooring.
It is relatively easy for a non-professional to install, and can be put down over a thin foam (floating floor) as required. It typically does not need to be nailed down, and is fairly resistant to humidity changes. Some of the newer types of engineered flooring have a "click 'n lock" feature that even does away with the need for glue. Engineered Oak flooring is typically bound to a bottom of ash or pine, which being softer woods, allows the subfloor to move about without creating the dreaded "squeaky floor" that solid wood floors can have.
Solid oak floors have been around since people were building castles, and it is hard to imagine a more beautiful, or permanent, thing to walk upon. They do need to be nailed down for a correct installation, and filled, and sanded, and stained, and finished in place. But, you end up with a floor that will be around for generations.
Solid oak flooring is thousands of times more durable that engineered laminated oak, it can be re-sanded over and over again, it can be refinished, and is easy to repair. It is not easily installed over a concrete foundation.
Engineered oak flooring is much more cost effective, can sometimes be sanded once or twice, and the repairs never look like the original floor. It is, however, easy to put over a level concrete surface using a foam pad or actually gluing it down with a construction adhesive. It also has the tendency to "buckle" under heavy weight, such as a large bed or dresser, and bow up. A nailed down solid oak floor would never do this.
A floating engineered oak floor can cost as little as 1/5th the total of having a solid floor installed! There are of course, a number of caveats:
Engineered floors are pre-finished, so color selection is by chip, not by any desired stain, so most custom colors are out.
These pre-finished floors are initially tougher than solid oak, but are hard to repair, if at all. (Don't believe the salespeople too much.)
The companies change their styles and colors often, make sure you buy enough for repairs down the road.
While solid floors impart a feeling of walking on a forest floor, engineered planks sound like you might be dropping ball bearings on a sheet of glass. Think of dog's nails, the kids playing basketball indoors, etc. The echo effect can be significant.
With solid oak flooring, you really have nothing to worry about, except for the cost and the ability to find a good installer. Solid oak also takes at least three times as long to install as an engineered product. It's messy to put in, the sanding will put oak dust in every single nook and cranny of your home, and the smell of the finish is pungent.
Solid oak flooring is a long term commitment. At least once per year, the floor will have to be "disced", which means unless you want to get good at floor refinishing, you'll need to re-hire the contractor to come out to do it. It does help if you put a small amount of the acrylic wood finish into your mop water as you do your floor cleaning throughout the year.
So, there you have it! You can go for the "fast and the pretty, but not long lasting", or the "permanent, but expensive."