I have one, and it may very well be for sale soon
The only way to really compare it, is to work out what you really need from your car. if you really need the extra seats and boot space then its a no brainer. The zed was perfect for me when I didn't need the extra seats or boot space, but the M3 is ideal for my needs now.
Spec wise, the SMG II is awesome and the extra power is very noticeable imo. The only thing that I'm not keen on is the noise, very tinny (not a real word ) and raspy, not as addictive as the V6.