Royal Princess or RCL Oasis??
 

Can't seem to decide between the two. Have sailed Princess twice and never with RCL, but have wanted to try Oasis or Allure. Any feedback would be great!!! The sailings have pretty much the same itinerary. 3 islands and 3 sea days in Dec-Jan. My husband and I are in our early 30's and love to cruise. What are your opinions??

If you want to try Oasis or Allure, then try it, particularly if you love to cruise. You seem to prefer big ships, so I don't think you'll be disappointed with either decision. I think the question is really what the choice of Princess ships is. There may be a price differential between the cruises depending on your cabin.

The Oasis class ships are like no other. I would say try them.

Sorry to bring this so sad news, CLM, but the Princess Cruises newest ship has some bad luck problems these days - power related mechanical (and probably electrical) issues. She is currently going to Barcelona from dry dock repairs.
Other than that, I would definitely choose Royal Princess over Oasis - for me Oasis is very very overated, and toooooo crowdy for me. Plus, the Royal ship as being the line's newest is well worthy of trying out, don't you think? ;)
You can read about the Royal Princess power lost incident here
http://www.shipcruise.org/royal-princess-itinerary/
The article also shows the ship's current position and its complete itinerary and sailing schedule as dates and prices for 2013-2014 and 2015.
Whatever you choose - good luck with prices, and have a great vacation! You simply can't go wrong with any of those ships anyway! :))))
PS: Book the Princess ship, ok? :)))))