You may get lots of different opinions on this. Going by your countdown, since you're going to be on a 7 night cruise on the Oasis in January, I would say go with the 4 night cruise on the Liberty. I will be on her sister ship, the Freedom, in October.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)