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I recommended you Lifetype. I am not a encoder but I readed (not remember where, herve´s post perhaps) that the wordpress code is bad.
I do not like admin section in Wordpress and Wordpress MU is a very young project. However, there are a lof of themes and plugins for WordPress and a lot of people use it.
Lifetype has few themes; less plugins that wordpress but it is enough for me.
It is a personal opinion: try both...and choice Lifetype, of course