What you have to decide first is whether or not you want a finish that is built up, and that you can feel, or one that seems to not be there at all. Straight tung oil, (maybe thinned a little with mineral spirits) is best for a natural finish that you can't really feel. But a tung oil "finish" with varnish resins or other hardeners would be used to build up multiple coats for final steel wool (or wetsanding) and paste waxing/buffing. If you're buying straight tung oil the brand is much less important, but for a tung oil finish there are some crappy ones. If you can find "General Finishes" (I think that's the name, I'm not at home right now) in the UK they have a good finish for building up on a body called Arm-R-Seal I think. I like their satin version because oil finishes can get a sheen to them in "high traffic" areas like the elbow and picking area. The satin seems to regulate that. Also if you have a porous wood like mahogany you'll be fine but if you're going over maple or something dense I would still thin out the first coat.