Have you used "SAP CRM On-Demand"? (their ASP offering) ?

I have no particular bias to any company but the three options you are choosing all have very different "styles" and models. SAP's on demand product was designed to be a stopgap from incursions by salesforce and they found that they kind of like the idea so they are moving forward with other modules. While it is functionally decent on the sales side, it doesn't offer much more than that. Salesforce.com is now more of a platform than anything else and has well over 300 plus modules that have been developed by their AppExchange community. Its upside is that you have the most sophisticated ondemand platform. It can get pricey if you need a lot of customization and modules, since each of the AppExchange partners has the right to price their own modules - though salesforce is alert to overpricing. SugarCRM is open source and has good functionality but their pricing is not a lot different than the licensed model - and in fact, though their open source idea sounds democratic, you can spend plenty with those guys. Their upside is that there is continously developing functionality and the core sales product (the for sale one) is solid. Frankly, for what you're looking for, SAP is probably the best but as the hybrid. I'm not aware of any of the three having an "inventory ondemand" product, though honestly, I haven't done the research over the last few months to know that.