I never noticed size differences of rides between WDW and DL, except for the Castle.
Comparing the WDW Castle to the Disneyland castle is kinda hard to do, considering the time difference that the two were made. I'm sure that if Walt had the money and found out that his Imagineering team could work it out, he would have made a bigger castle, but the reason its so small is so that you can't see it anywhere else in the park (besides Fantasyland and Main Street) to destract from the theming of the other lands. The Imagineers working on WDW's castle decided that it would be best to make the castle as big as possible so that visitors driving there could see it (and know that its there). With the budget they were working with, its no surprise that DL got a smaller castle.
Heres an interesting thing I learned: On each of the "peaks" of Sleeping Beauty Castle, there are golden spiers on top, except for one. When designing the castle, Walt wanted golden spiers on each of the peaks, but Roy went nuts when he heard this, as it was way too expensive, with the budget they had. Walt went ahead and had them put on anyway, but he had one ugly, non-gold spier put on one of the peaks, and told Roy "There, that can be your's!" See if you can find it if you ever visit the park
I agree with everyone else that the rides are much better at DL, plus, at Christmas, IASW and the Haunted Mansion have holiday versions of their rides. DL also has more rides than WDW, like Pinnoccio, Roger Rabbit (My fav), Alice in Wonderland, Mr. Toad, Indy (this and Dinosaur use the same track, but Indy uses it much, much better), and a few other Fantasyland rides.
To me, Tomorrowland at DL isnt as good as the one at WDW, though.
Much of the best of WDW is and is going to be at Disneyland, but often copies are never as good as the original...
The thing about the sizes between the two, it really depends what you are looking for. WDW is great because of how huge it is, but DL is making good use of its small size, and makes it possibe for guests to simply walk from each park to Downtown Disney to the hotels. I thought that aspect of DL was kinda cool. It almost makes the monorail obsolete, unless you just want to ride it for fun.
Its hard to choose between the two...I like WDW, but after going there so much, its nice to have a change, which is why I had so much fun at DL last year. If you havent been to either, Id say go to WDW first.