DiggleNamer 0 Light Poster

If you want to have a different template for certain sections of your web site, that use different templates is the best way to use Wordpress MU? I did that for:

http://example.com/
http://example.com/spas/
http://example.com/massage/

But I have a feeling this is not good for SEO as the three sites have different site maps. Would i have been better off just doing subdomains?

I am going to do a new site which will use a wordpress directory site (i cant use just a different page template as it is a detailed directory software) on one section and I want to know if I should do it as a sub, or use wordpress MU again:

www.example.com
www.example.com/directory