I think it comes down to money, I've used AIMS for many years and i'm presently using RM - both are very very good (in their own ways!) but both are very expensive. I don't think you can really compare AIMS with Geneva...
I've had a demo of Geneva, basically because I couldn't believe the price they were offering it to us for, and basically - you do get what you pay for.
Saying that - Astraeus seem very happy with it, have a search back a few days - CrashDive Of AEU has written an IT comparison from an AIMS v Geneva point of view.