Ehhh, Battlefront does have more levels, currently, but coming this summer, there will be plenty new levels to match it up a bit more on quantity.
As for fun-to each his own. I do thoroughly enjoy Battlefront, but I think I would still say I like Halo 2 better. While the environments may be a bit more diverse, you still end up doing the same thing over and over again, to a far greater extent than in H2. Plus getting a kill the BF is SO much easier than in H2, giving me a greater sense of accomplishment.