MX Guarddog vs DreamHost Spam Filters

Does anyone have any experience with MX Guarddog spam blocking service and have any opinions as to how it compares with DreamHost’s provided anti-spam service? They seem to get good reviews online. Currently I’m using SpamSieve with my Mac’s email client, which does nothing when I’m using my iPhone or iPad, so I want to use something that hits the spam at the server end of things.

Thanks in advance!