Another factor is Liseberg doesn't staple you (or at least they didn't in 2009) like Six Flags does. I found the airtime on Balder to be a lot more enjoyable as a result.
For me there is no comparison between the two: Balder kicks El Toro's ass. El Toro has a great start (stronger than any sequence on Balder), but then loses a lot of steam. Balder kicks your ass with punchy airtime throughout the entire circuit. El Toro is, of course, really good too though.