There is no answer for this popular question.
The Olympus series are by far the most popular cameras for underwater use. Olympus has done a good job of providing excellent cameras and an inexpensive and capable housing that has allowed those interested in UW photography to get a complete system for several hundreds of dollars cheaper than other brand cameras.
In the right hands, both cameras yield excellent results. I would challenge anyone to champion one as the best. They both deliver excellent results.
I chose the cp5000 over a year ago for several main reasons:
1. wider lens........28 vs 35
2. wired strobes vs. fiber optic or wireless
3. macro to 3/4" without add-on lens
4. already had a 4040 and the 5050 wasn't out yet
The cp5000 was out almost a year before the 5050 was introduced. The 5050's feature list now matches the cp5000 and has better battery life.
I believe both cameras are out of production, but many are still available. The newer digicams are being introduced with features that aren't improvements for underwater use.
A problem for a new buyer.
Like I said, there isn't an answer to this question. You'll be happy with either system in my opinion.
Karl