Zbrush is great although it has a learning curve similar to Terragen (lol). Your uv package will depend a lot on what kind of models you need to texture. Theres two elements at play here, the creation of the UV maps themselves and the painting of those maps. The map creation happens within a modeling package and defines where each polygon is placed on a square grid, this can be generally planar (x, y, z), cylindrical, spherical, and "atlas" (a term used in Lightwave, don't know what other packages would call it). This grid then forms the basis of where textures fall back onto your model. "Atlas" mapping is an unwrap of your model, either continuous (all polys connected on the grid), or dis-continuous (front, back, sides, top, bottom and distinct areas mapped separately over the grid). Depending on your model you would use a different mapping technique for different parts, for example your dragons wings could be mapped in the fully extended position as a planar in the y axis and for the main part of its body mapped in a cylindrical projection down the z axis. Care must be taken to ensure that where the uv maps join (wings to body for example), the textures line up. This is where a bespoke UV painting program comes into play allowing you to paint directly onto your model and saving out a textured grid that you can then map back onto your model in your rendering package. The trouble with most UV painting packages is that they are only as good as the uv's they are working on and that is down to the modeling package they were created in and the person doing the modeling. Messy modeling makes messy maps. I personally try to use as simple projection as I can and paint up my textures in Photoshop, do some renders and then do some further tweaks in photoshop to get the final alignment bang on. One method is to make the first texture you apply to your UV map a simple coloured checkerboard so you can easily see what lies where. You can then make any adjustments as necessary and paint your final textures over your lined up checkerboard. I'm sure silo supports UV mapping and I would suggest sticking with that for the time being and using photoshop or similar for your actual texture painting.
Bit of a rant there but I hope it helps
Richard