Thanks for those replies, maybe I need to rewrite my question, especially in line with the response on another thread...
Your choice is just about right. Toolbox comes, in a way, as a newer and modernized Sandbox, coded in HTML5 with latest web practices in mind. Toolbox would be a more solid and forward looking choice for you to start with.
So Toolbox has gone, underscore isn't arriving yet... and I'm not sure I want to head back to Sandbox.
The recent email regarding business websites was interesting, but I'm not sure if there is a good generic business theme. Some specific business types are well catered for, but I need a theme for a business who have virtually no photos ( so there goes the portfolios), no products (it's a service industry) and will write few posts other than the occasional news items. They want it quick, cheap and easy to use themselves. WordPress.com fits, but picking a theme which works isn't easy, especially if we only have Sandbox as a framework theme. Suggestions?