The less opaque the finish, the shorter the lifespan. Get used to a lifetime of constant restaining if you want a clear or transparent finish on wood - regardless of brand. If it were me, I'd go with a solid stain and save the maintenance headache.

I'm aware of the re-staining frequency with semi-transparent. I'm just trying to figure out what the best stain to use is. Am I more likely to get 5 years from one and 3 from another?

Ok, I found some stuff which might interest you in previous threads on the Old House forum of Gardenweb.

It is about the Onion house. Take a look at the discussion of the options, the durability discussion. Link below.

Here is a link that might be useful: Onion House cedar shingles stain etc

I still haven't found anything very useful, but I did come across an article posted on the Armstrong Clark site that might be useful to some in this predicament:

http://www.armclark.com/html/article_semitrans.html