I have experience only with the Helmsman varnish, but I'm under the impression that the other two are penetrating finishes rather than surface films. Assuming that's correct, the varnish would probably offer more protection from moisture but be considerably less pleasant to repair when it finally fails. Penetrating finishes probably need more frequent maintenance, but that maintenance is likely to be much easier.

Thin down the paint a bit for the first coats. The final coat should blend in as long as you don't go back over an area once it's been brushed. Or you may rather like the routine of semiannual cleaning and re-application of a penetrating oil.

I used Sikkens stain on the exterior of my log home. I am under the impression, that it only needs to be sprayed down with a hose and water once a year to keep it looking new. Every 8 years a recoat of stain. I sprayed, the stain on, but you can also roll it. It quite expensive, about $75 a gallon, but worth the money if your not touching it up every year. I used Teak, heres a photo to get any idea.