My two cents is the note 10.1 is cool but dated.... The nexus 10 is a sign of tablets to come. I love my note2 and will be holding out for the next version of the note 10.
Something bothers me buying that expensive of a tablet and it has specs lower than my phone.... I kinda expect the tablet to be the powerhouse and my phone to get the job done.
And my two cents between all 3 just quickly....
Apple-ios familiarity, great screen, and great external design
Note 10.1- great concept but dated, low screen resolution, under powered, and the spen is nice, it was awesome when it first came out
Nexus 10- the tablet that was thrown together to show what an android tablet should be. As it stands my personal opinion is with proper apps the nexus 10 is top if you are familiar with android.
If the nexus 10 had spen and external sd I would buy one in a second.... But then that would make it a non nexus device but you get my point.
I am a spec whore and I defend that with high end equipment means long term use ability (most of the time). I don't buy things that are good for now... I buy top of the line so in a few years they are just dated instead of completely obsolete. As of now the note 10.1 is getting dated.
I know it's a tablet but I would love to see a removable battery but I realize that not happening and so I don't really put much thought into that.
Also I think this year will be interesting for Android so unless you need it now... Give it a little time.