Within Temptation and After Forever are both talented bands, make no mistake about it. I respect both bands, but in my opinion Within Temptation are superior. This has nothing to do with who a better singer is or which band plays better instruments. It simply has to do with WT having better songs and songwriting and variety. You can listen to AF and although it's good, you can't help but feel like one song is just an exact copy of the next as far as the operatic vocals are concerned. Even Epica and Nightwish mix it up, but from my limited experience with AF and I could be wrong, but from what I heard every song seemed it like it never ended and it was the same thing for the entire length of the disc, and any Video I've seen just confirmed this trait. I mean no disrespect but it turns into dull whine when you listen to them for an extended period of time.
Within Temptation has catchy melodies and stands on their own in the sea of cookie cutter Nightwish bands and B&B clones. Also they have an owl in their video, shit..they win just for that lol.
Just please keep in mind I'm not trying to bash AF or troll / piss anyone off here, I'm just trying to be objective with my opinion. As far as I'm concerned I would love to see either one or both, but if I had to choose it would be Within Temptation as I am clearly more drawn to their sound.