I've said it before and I'll say it again, Wii owners should only buy World Tour...don't waste your time or money on RB 1 or RB 2. For everyone else get World Tour if you don't have RB yet, and if you have RB already (and you're not a Wii owner) you have a choice (I would lean towards RB2 though).
The two major complaints from RB fans about GH3/Aero was first that songs were "overcharted" and second that they didn't like the songs chosen for the game. The music editor solves both problems and is really an impressive piece of tech (1, 2, 3). Add to that an extreme level of customization for character animations, venue lighting, custom tattoo art, etc...and its clear the folks at GH went a cut above what RB2 is offering in terms of features. And obviously any difference in song preferences is made up for by the editor and GHTunes community.
The reason RB owners have a tough choice is that in a year RB3 will probably release with an editor that is just as (or more) robust and it doesn't make a lot of sense to spend big bucks on two sets of instruments. So if you own a PS3 or 360 and RB then you should get RB2 and wait for RB3 to jump in on the editor goodness. Pretty much any other scenario and you should buy World Tour.