PLUTO appears to be very new, and there doesn't appear to be a lot of documentation. So I would be concerned that you'd be working through a decent number of bugs to get things working. utPLSQL has been around for a number of years and pretty widely deployed, so there have been a lot more bug fixes and a lot more people who can help out if you run into problems.
Additionally, and not to disparage anyone, but Steven Feuerstein, who wrote utPLSQL is one of the most recognized PL/SQL experts in the world. While I'm sure the author of PLUTO is a perfectly competent developer, I don't believe he has anywhere near the reputation Steven has.