Like the others have said, personal prefferance plays a large part.
You have to consider where you will be in 6-12 months.
No point building a massive state of the art bench, then moving into a 1 bedroom squat!!
Mine used to be a massive thing, but then I got tired of all the space, and made it the size of a normal desk, and attached a spray booth to one side.
Now, no matter where I live, I can build models in my self contained bench.