I have been looking into the same question. It is a pretty tricky question. This is what I gather. Semi-transparent stains allow you to see the grain of the wood and have less pigment in them. They penetrate better and are less likely to peel, but having less pigment they also have less UV resistance and don't last as long as semi-solid or solid color stains. Solid color stains hold up to UV longer and therefore last longer, but if put on too heavily they can peel off just like paint. We tried a semi-solid stain, and, even knowing the above, put it on too heavily. Looks good ( no UV damage ), but already starting to flake off in some areas. The best sounding system I have heard of is made by Timber Pro and is a two part process where the first coat penetrates deeply and molecularly bonds with the wood. The second coat bonds to the first and is basically a semi-transparent stain. The first coat protects the wood, supposedly forever, second coat wears off and needs replacing pretty fast, 1-2 years I think, depending.