You probably know this, but TS skill is not something that employers look for. It's Lightwave and/or 3DSMax. I'd say if you're getting TS for the modeling experience (wich it is good for) get an earlier version at a more reasonable price.
Actually, there ARE quite a few employers that accept tS experience instead of MAX - the idea is taht if you understand the basics of one 3D program, learning another is just knowing how to reapply what you''ve learned on another program. Also, quite a few smaller development houses use tS, such as those basing their work on the Genesis3D engine. There are a number of plugins that allow direct export of tS models, scene and animations to to the Genesis 3D object and animation formats.
Also, if you''re looking to do pre-rendererd work rather that real time, it doesn''t matter what application you use, as long as you end up with impressive results. Check out the most recent Caligari (makers of tS) gallery images to see what tS4 is capable of.
As for which version to choose, I''d say tS4. More features than 3, and the new render engine is well worth the price. You can always download the demo and decide for yourself.