For a first time using nandrolone I'd opt for NPP that way if you get unwanted side effects you can end your use of the compound and have it out of your system much faster.
If you get sides with deca you're potentially stuck with them for a few weeks. Nandrolone can give some guys depression. I've experienced it. It's a gloomy, meh, blah feeling. Anyway, I like the option of getting back to normal sooner than later. Once you see how you respond to nandrolone you can always use deca in a future run.
NPP you want to inject it EOD or at least Mon, Wed and Fri.
Deca you only need to inject it once a wk but many people inject it twice a wk since they are injecting their Test E or C twice a wk anyway.