Rock Band 2. Guitar Hero World Tour is obsolete, no more DLC for it (maybe you meant GH5?). Band Hero, is a kinda family friendly version as far as I know, I haven't actually played it. Rock Band 2 still has DLC coming out all the time, Rock Band 1 is compatible (you can import most of the songs into RB2).
I found GHWT and RB2 comparable games-wise, but others have felt differently.
I have Guitar Hero World Tour, Guitar Hero Metallica, Rock Band, and Rock Band 2. I enjoy playing all four, but I do tend to find that the Rock Band games have slightly better note charting. I also initially found the Rock Band games a little less forgiving for hitting the notes, but thats not such an issue anymore.
To a large degree I think it comes down to song preference. In that area I've tended to find that the Guitar Hero series satisifies my metal/alternative oriented musical tastes a bit better. In fact, I only purchased Rock Band 2 because it was significantly cheaper than Guitar Hero 5 at the time (which has since dropped considerably in price). I had intended to purchase GH5 instead, as the song list seemed more my taste.
The Rock Band series seem to have a much better selection of DLC, if you want to extend your musical library later, and I find the Rock Band guitar controller to be slightly easier to use than the one that shipped with Guitar Hero World tour (I have no experience with the latest GH controller though). In particular, I find it easier to hit the 5th fret note, as the fret buttons are flush and a little smaller in width.
Rock Band 2, no doubt. I've had an American version for a long time now and just swear by it, I also own GH:Metallica, and had previously played the GH series for a long time. Theres just lots of little things that are better when you're playing, its easier to see you Overdrive meter without changing focus from the notes chart, its easier to see how you're performing as a whole with the Stars sound and graphic, and of course the DLC can't be beat.