James I have used them both but own the spaceball. I think that they are both great to use but I still don't find them easy on my hand after a while of using them after a while. The spaceball itself has a ton of buttons you can program for different things, you can program the buttons so that you can use it in MS applications, the program that it comes with has standard things in it like scroll etc..
I like the space traveler for the size, the buttons on that are around the base not as many as the ball, and is nice when working on a laptop because you find that the spaceball takes up way too much space. I never programmed the traveler I am sure that they have similar tools for that. The spaceball I have now is sitting off to the side because I lack the room around my computer, just too much crap...
I have found that UG needs a spaceball because its difficult to manipulate the models, PROE is not bad at all and thats why the ball is sitting there with dust might I add. I conteplate about getting the traveler for my laptop but its alot of money to get it and just not use it.
For a desktop environment in your office the spaceball is the right choice. It is intended for intensive and long term use, not for traveling.It has a convenient ergonomic rest-pad for the palm of your hands. This one can be mounted on both sides for left and right hand use. The ball itself is covered with rubber to ensure a good grip. It's perfect ball shape enables you to move your fingers under it and lift it, instead of squeezing it and pulling it up as with the traveller. The device should be operated with your fingertips, not with your entire hand. The programmable buttons are easy within reach with your little finger and thumb, without have to move your other fingers. Make sure you program the shift and ctrl-key under 5 and 6.
And yes, it is big, but my desk is too. If your desk isn't, than that is a general problem.
Your can order them along with your new Dell System: cheaper.