What is the best WP host given these circumstances?

I'm looking to build a multi-site that will use the AutoBlog and MultiDB plugins (among others, but the idea is reliant on those two playing nicely together).

As with all projects, it will start small but hopefully grow; I would need clear and easy upgrade paths beyond the basic plan that I would use to get things started.

All of my other sites are small with low traffic and I have been fine with GoDaddy but I feel this project needs something more robust, quick and scaleable.