I believe the owners manual will probably state 50 hours, probably best to follow the JD guidelines.
This is pretty much a topic that has been discussed many times before. There has been speculation that JD has put in break-in oil and such in their engines and that you should wait to the 50 hour mark.
I highly doubt there is break-in oil in the engines unless they don't drain them after testing that they run at the factory. And if the latter is true, I would change it as soon as I got it home (if I had it to do all over again). That all being said I changed mine at 50 hours following the manual specifications.
As for running JD oil, it also has been speculated that they wouldn't sell a bad oil. Truth be known, their oil is an adequate oil (9 times out of 10, you will sail through the warranty period without issue and probably even years afterwards.)
There is most definitely better oils out there. Do you need them? Probably not in normal/most conditions. It really just depends on how the equipment is treated by you and the other factors that are out of your control (temperature , humidity, and other forces you can not control.)