Water-based polyurethanes provide a clear finish and have low odor. You can recoat them in two hours and clean your tools with water. If you start early enough in the day, you can apply the recommended four coats and sleep in the room that night.
Oil-based polyurethanes leave an amber glow and require fewer coats. But the five-hour wait between coats and 12-hour wait after the last coat will put a bedroom out of commission for a few days—and you'll have to put up with a strong odor.
Both water based and oil based poly offer good protection; the biggest difference is in appearance. If you love the natural look of maple, apply a water-based (waterborne) polyurethane. They appear milky in the can, but go on clear and remain clear. They'll slightly accent the character of your wood without giving it the amber tint of an oil-based poly. (However, some woods, like the oak shown, cry out for that amber tint.) Water-based finishes dry fast—most within two hours—so you can apply several coats in a day and use the room that night. They have minimal odor and clean up with water too.
But water-based polys have their tradeoffs. They cost twice as much as oil-based polys. They won't give wood the rich glow that oil-based polys impart; some even consider them cold looking. When I applied waterborne poly recently, I found that it went on so clear I had to use a bottle cap to mark each 8-in. wide swath of finish as I went.
Most water-based polys contain only 30 to 35 percent solids, compared with the 45 to 50 percent solids in oil-based products. Since these solids create the protective finish, you need to apply four coats, as opposed to two or three. And you may need to apply additional coats every two years or so.
There's debate over which finish is harder, but some experts maintain that hardness isn't necessarily a good attribute of a floor finish. You want a finish that will flex along with the floor. And a super-hard finish shows scratches more readily. You'll prolong the protective life of any finish by eliminating its No. 1 enemies: dirt and grit. Sweep or vacuum the floor often and put throw rugs in high-traffic areas.