It really depends. That said, most great inventions (and by great I mean they sold a lot) are handled by an existing company that has a distribution network already in place and can take your idea and make it great. Take for example the two ball putter from Calloway. Imagine trying to break into the golf market place and sell millions of them if you were by yourself.
Here's another lesson to take from that example: The inventor took a one-time payment up front rather than sharing in the overall revenue. Big mistake . . .
That said, take a look at the Leatherman -- a really great tool kit in one item that has created a massive empire. Both ways work.
A rule of thumb is that if it will be easy and relatively cheap to get it to market and you believe you can sell millions of them for many years to come, then invest up front and go it alone. If not, (and in most cases it's not) work with a bigger company.
All the Best