What is your preferred SEO Hosting provider?

I'm using seohost.com at the moment (recommendation by Becker/Source Wave) - I have 50 sites at $100 p/m at the moment. I will need to double that to accommodate the new domains I'm buying, however it's an opportune time for me to establish what other seo host providers are available.

I'd be interested to hear about who you prefer, and what your experience has been.

Thank you!