If the object here is to recommend a finish for a hardwood floor that the poster can put on themselves, then I'm sure all of the knowledgeable people in here will have recommendations that will serve the poster well.
If the objective here is to recommend a finish for a hardwood floor that will be the MOST durable and last the longest, then we have to go with relatively new technology that the original poster probably shouldn't try to put on themselves.
The most durable coating for any surface will be the one that both:
a) sticks to it well, and
b) dries to the hardest film.
...cuz it's the hardness of the coating over a wood floor that protects the wood and determines how quicly that floor starts to show "traffic patterns" from dirt becoming embedded in the floor (or the finish on the floor) from the foot falls of human traffic. The harder the coating, the less dirt becomes embedded in it, and the longer it takes for traffic patterns to start to show. Therefore, the harder the coating over a wood floor, the longer that wood floor will retain it's "new" appearance, and the more slowly it will loose that newly refinished appearance. That makes some kinda horse sense, doesn't it?
The standard test to determine the hardness of a coating is something called a "Taber abrasion test". Google Taber abrasion test and you'll see all kinds of references to this kind of test.
I don't know what this Osmo Polyx-Oil stuff is, but there is a new kind of polyurethane working it's way down the pipes into consumer products that most people are probably unaware of called catalyzed "waterborne polyurethanes".
Lemme start off by saying that there are more kinds of waterborne polyurethane chemistries in coatings than you can shake a stick at. The kind I'm talking about require a catalyst to be added to a water based solution of isocyanates and glycerine before being spread on the floor. The resulting coating is about 3 times as hard as the conventional oil based "polyurethanes" that have become the standard for finishing hardwood floors since about 1956. Basically, these new generations of "catalyzed waterborne polyurethanes" have about the same durability as an epoxy concrete floor paint.
One example of this new technology is a product called "Traffic" marketed by the Bona Company of Italy. The problem with Traffic is that once you add the catalyst, then that liquid inside that gallon jug is going to harden up on you over the next several hours no matter what problem you run into, so it's not very user friendly. Bona also markets another hardwood floor coating called MEGA, which somehow allows you to put the coating on, and save whatever you don't use for a future application. I don't know how it MEGA works. Both are considerably harder than conventional oil based polyurethanes, and would therefore be expected to provide much better service than could be expected from a conventional oil based polyurethane on that fact alone.
http://www.savinobrothers.com/taber.htm
In the above web site, the brown can with "Woodline Polyurethane" written on it in white lettering is the Taber abrasion test results for Bona's own oil based polyurethane. (Which is a technology that's been around since 1956 when the first polyurethanes were patented by the Bayer Company (the Aspirin people) and who are still a major supplier of alkyd and polyurethane resins to the coating manufacturing sector of the economy.)
http://www.gustafsonwoodfloors.com/bonikemi.php
It should be noted that the only polyurethane that even comes close to Traffic is the moisture cure polyurethane from Polo Platz in this web site. Moisture cure polyurethanes are generally considered "industrial coatings", not residential floor finishes. The biggest North American manufacturer of moisture cure polyurethane coatings is Wasser.
http://www.wassercoatings.com/
http://www.bonakemi.com/productspecs/pdf/traffic.pdf
The French chemical company Rhodia explains the chemistry of moisture cure polyurethanes on their web site, but they don't explain the chemistry of these new catalyzed waterborme polyurethanes like Traffic:
http://www.coatings.us.rhodia.com/chemistry.asp
If anyone wants to know more about the chemistry of conventional alkyd based polyurethane "varnishes", post and I will answer. If anyone wants to know more about moisture cure polyurethane coatings and why they're so much harder than conventional "alkyd based polyurethane "varnishes"", post and I will try to answer. I really don't know anything about the chemistry of catalyzed waterborne polyurethanes coatings like this "Traffic" product, but I do know it's extremely hard and durable, and that's what you need to keep a floor looking good for a long long time.
I think it's also best to have products like Traffic and moisture cure polyurethanes installed by professionals with experience using them. These are very correctly considered industrial coatings, and simply aren't as user friendly as the oil based polyurethane varnishes that DIY'ers are used to using. These new generation of polyurethanes are almost as hard as powder coatings like the enamel on a steel bathtub.
PS:
Powder coatings are also called "Porcelain Enamel". Probably the hardest coating that most people have in their homes is the porcelain enamel on the inside of their ovens. This is a special kind of powder coating that's baked on at about 1300 degrees F, and is called a "ceramic coating". For more info on baked-on coatings, visit the Porcelain Enamel Institute at:
http://www.porcelainenamel.com