For me the best is WP Robot. I've tried Auto Blog Samurai and although it's OK it requires a client application and it's scheduling isn't something I like.
WP Robot has about 19 modules including Amazon (I love that one), article,yahoo answers, Flickr and many more.
Because it uses templates some knowledge of HTML is neccessary to modify them (It's a good idea to create unique templates to avoid a footprint the search engines could find)
Support is pretty good and they update the software often. The only snag is it's about $169 for all the modules and unlimited license. As I recall I think if you Google WP Robot coupons you should be able to get it at a discount.
Ohh and talking of footprints if you buy it rename the WP3Robot plugin directory to something else.
I have it installed on about 8 Blogs and haven't had a problem with it.
I use it to post only 1-2 posts a day at most and I keep an eye on the Blogs a couple of times a week. I also add some unique content in every now and then to stop the Blog looking to spammy.
As to 5 Auto Blogs on one host posting 100+ per day I don't know it'll depend on your host. If you have a VPS / Private server you should be OK.
