Of course, many people have already posted similar replies, but here is my take:
I have seen both the Broadway company and the First Nat'l Tour a total of 4 times. The Broadway production definately has more scenery around the proscenium that in a way extends around part of the audience. (There are many vines, gears, spooky lights, etc). On Broadway, the dragon's wings are a slightly different shape than the tour, perhaps a little bigger, but not by much. Also, the dragon on Broadway has visible ropes tied to it that animate it, where the tour's dragon is not controlled by ropes.
On the tour, the proscenium is brought into the theatre it plays at, and consists of various gears/cogs, and a large speaker on either side covered with vines. Another difference between the productions is that the Broadway stage is raked (on a slight tilt), and no other production is. (This does not in any way effect the quality of the show.) Also, on the tour, the groves in the stage that carry scenery on and off are slightly different. Also, on Broadway, the monkeys fly out over the audience at one point, they fly around on stage in the tours.
In the first national tour, the only differences from the Broadway show are the ones describes above. Practically everything that happens within the prosceneum is exactly the way it is in New York (aside from the fact that on Broadway, Elphaba rises from a hole in the stage for "No Good Deed" as opposed to on tour, where she runs on). Both productions are equally spectacular.
As for the 2nd tour, I have not seen it, but have seen youtube clips and pictures enough to be able to describe it well to you.
The second tour is built to play in smaller cities (not nessecarily smaller theatres, as many believe). The set for the second national tour has two wooden panels that have pictures on gears/cogs painted on them (in addition to a smaller proscenium with actual gears/cogs). The dragon is designed in the same way as it is on the first tour (perhaps a tiny bit smaller). However, in some theatres, depending on where you sit is certain theatres, you view of Elphaba flying can be obstrucked by the dragon's head. Also, the deck (the stage that is brought in with the show) is thinner than that of the 1st tour or Broadway. Also, the 2nd tour has a smaller orchestra and some smaller set peices that do not function as fully as their counterparts on the 1st tour or Broadway do. This is not to say that you shouldn't see the 2nd tour, of course you should if you get the chance; it is still a spectacle!
In terms of actors and actresses, all productions are equal. In fact, many performers move from cast to cast.
Hope this has been helpful!
"Brevity is the soul of wit"--Hamlet