BeoLab 9s are excellent IMO. If you listen to a lot of poorly recorded material, then I would choose them over BeoLab 5s. 9s do a very good job of sounding detailed and transparent without revealing every flaw in the recording. Very good for electronica due to the powerful/extended/detailed bass.
BeoLab 5s are IMO much better, as long as you don't spend most of your time listening to poor recordings. They present the recording as it exists and are completely unforgiving when it comes to reproduction. If your recording sound awful - the speakers will make it sound awful! For a lot of electronica though, you don't need to worry, and almost all the electronica I've heard on BeoLab 5s has been undoubtedly better than 9s.
Only a home demo can really tell you which will sound better in your space...
