Very good question. As with anything in the MCAD marketplace, there are multiple vendors addressing the same question. Since you have a familiarity with iLogic (now AutoDesk Inventor ETO), I will focus on the DriveWorks side of things.
[In the interest of full disclosure, Razorleaf corporation is an Enterprise Services Partner for DriveWorks as well as a member of the AutoDesk Developers Network. We do not, however, sell any design automation or CAD software.]
The primary difference is that DriveWorks is a SolidWorks Gold Solution Partner designed to drive SolidWorks models while Inventor ETO is an AutoDesk product that runs inside of Inventor. DriveWorks is available in several "tiers." You can browse the details at their website www.driveworks.co.uk but the short version is that DriveWorks Xpress is a tool that is available to all SolidWorks users in the core SolidWorks product under the Tools menu. This allows you to drive SolidWorks parts and drawings by inputting values that you specify (i.e. you can input a pressure, you don't have to know the final dimension values), defining rules to determine the outputs and mapping to the SolidWorks model parameters. DriveWorks Xpress will then create a unique set of files, rather than cramming massive amounts of configurations into a single monolithic file, like the Configuration Publisher will. The tool is incredibly simple, and to be blunt, it's designed to make you understand and fall in love with design automation. And it does a wonderful job because it's not just a demo, but rather a fully functional tool that many people use rather successfully on a daily basis.
DriveWorks Solo is a tool that runs inside of SolidWorks similar to DriveWorks Xpress but introduces the ability to create much nicer and more powerful user interfaces, drive assembly models and their drawings, automate the control and look/feel of the drawings and allows users to update the solid models live in SolidWorks as they are filling in the forms. It is a very competitively priced (pronounced "pretty cheap") option to get started in design automation. For many, this is all that they need. If all you're after is a tool to help your engineers and other SolidWorks users pump out designs and drawings faster, then there's no need to go further up the DriveWorks chain.
DriveWorks Pro shifts the tool from being engineering-focused to being fully featured. You have the ability to run independent of SoildWorks and, with an optional web server, in a browser window on an Intranet or over "the Interwebs." This means that you can now use the tool as a Sales Configurator as well as an engineering tool. It also adds a workflow functionality that allows you to use it as both for the same project so that sales can use it, then hand off the quote with all of its information to engineering for final design. The other big difference with DriveWorks Pro is the ability to generate non-CAD documents like Word quotes, Excel Bills of Materials, outputs to XML or SQL or ODBC databases to synchronize (yes, you can go the other way too) with ERP and other enterprise systems, and so on. Pro also provides an API, so realistically, if you know programming or a service provider, you can pretty much do anything.
So that's the rundown on the different DriveWorks products. If you're using automation to decide between SolidWorks and AutoDesk Inventor, then we can get into the differences between the approaches of the two tools. But for most companies, switching CAD isn't as easy of an option, so that's typically the deciding factor.
Paul Gimbel, CSWP
Business Process Sherpa