The other oil finish I favor is walnut oil, available from grocery stores for making salad. It polymerizes pretty well too.
That's really not the type of walnut oil you want to use for a finish. If you want to use walnut oil, my suggestion is to get
Mahoney's Polymerized Walnut Oil.
Mike Mahoney is a bowl turner and developed the finish for his bowls and sells it to other wood workers. It is a food-safe finish. I use it on cutting boards. Once you have the wood fully saturated and the pores filled in the board, all you have to do is wash the board and apply a new coat about 2-3 times a year.
The way to apply it is to flood the surface and let it sit for an hour and then wipe it off. With cutting boards, the first 3-4 coats will fill the wood pores with this method.
One of the things Mahoney's will do with cracks in cutting boards is cause the wood to swell and the crack will close. I have "rescued" several cutting boards with cracks up to 1/16-inch wide by filling the cracks once a day with Mahoney's oil over about a one week period. At the end of 7-10 days the crack appears as a faint line because the wood has swelled shut. I have never had a crack reopen in a board after it has been treated. It is, in effect, a permanent repair.
Mike Mahoney also has an oil/wax finish available. It is a mixture of Mahoney's Walnut Oil and beeswax. I have used the oil/wax on wooden salad bowls and on soapstone countertops as it is the perfect finish for those materials.
Oil finishes seldom are as good as man-made products like polyurethane in terms of durability and water resistance.
I would disagree with that statement. Polyurethane is quick and easy to apply but it is not superior to something like Epifanes varnish or Waterlox. Both Epifanes and Waterlox are a tung oil / phenolic resin finishes. These are far different than a standard alkyd-based clear "varnish" finish.
Polyurethanes (especially water based polyurethane) have supplanted traditional oil varnishes in industrial uses because of VOC considerations, and quicker drying times. They make a very good finish for kitchen cabinets and furniture as they are easy to apply and dry rapidly, while still giving good water resistance.
One of the great features of polyurethane varnish finishes is the wide range of surfaces: dead matte, satin, semi-gloss, and glossy. You cannot find that range of finishes available in an oil varnish finish.
One of the failings of polyurethane varnish finishes is very poor UV resistance. They become cloudy under heavy UV exposure and often yellow badly.
Other urethane based finishes that use catalysts (mainly automotive and industrial paint finishes) are a totally different type of finish and are meant as surface finishes on impermeable materials. For those uses, I would agree that urethane is a better finish.
Waterlox is a little bit thinner than Epifanes varnish and is easier to use as a wiping finish, but either will be superior to a polyurethane varnish on wood.
There are some additives in Waterlox that make it different than Epifanes. Epifanes is a true varnish and requires sanding between coats in order for the next coat to adhere. Waterlox will adhere to itself and does not require sanding - although, most people generally lightly sand between coats to eliminate dust nibs and other surface imperfections.
Both Epifanes and Waterlox need to be thinned prior to use. For Epifanes, the preferred thinner is the Epifanes Thinner that is formulated specifically for the varnish. Waterlox really needs a thinner with more solvent power than mineral spirits. Either turpentine, VM&P naphtha, or Epifanes Thinner will work much better than mineral spirits.
Polyurethane never penetrates as well as either Epifanes or Waterlox and the final surface film is not nearly as hard. That's why polyurethanes have not supplanted varnishes like Epifanes for bright work on boats or, in the case of classic wooden boats, varnishing the entire boat.
Both Epifanes and Waterlox benefit from using Epifanes Accelerator in small quantities. The accelerator actually seems to help the consistency of the liquid by reducing the surface tension (making a smoother coating) and also guarantees that the finish will be cured within 24 hours.
I have used the accelerator with Waterlox under rather extreme conditions of 90+ degree heat and very low humidity. In those conditions, I have been able to put on two coats per day as the accelerator will fully cure the Waterlox in about six hours.
It would not be advisable to do that with a brushed finish as the varnish may not have time to fully level. However, with a wiped finish there is no problem as the finish never has to level.
An easy to apply, oil-like finish, is Deks Olje. Deks is a unique product that applies like an oil but gets harder than an oil finish. It never builds to a high solids finish. Deks is a popular product to use on boat railings as it is easy to put on and easy to repair. Unlike cured varnish, Deks will adhere to itself without sanding. This is the characteristic that makes it so easy to use on railings. To renew the finish, all you have to do is wipe down the railing with a new coat.