A translation service provider's first concern should be compatibility. You need to be compatible with your client's formats, tools and workflow. If most of your clients produce documents with Microsoft Office, then by all means make sure that you have access to one or more Office licences, preferably in all popular flavours (2007, 2003, XP).
Likewise, if 80 percent of your (potential) clients use Trados, then investing in the same Trados version should be your number one priority. If other CAT tools like Star Transit, MemoQ or Across are leading in your market niche, then don't hesitate to choose the best match.
Most translation tools claim compatibility with one another, usually through standards such as TMX or XLIFF. But in my experience, the average translation project is already complex enough, even if the same version of the same tool is used by all parties involved in the process. Any additional conversion steps from one tool or format to another may cause unnecessary trouble, delays, or data corruption.
If you're a service provider, the inherent qualities or price of a tool only represent secondary reasons to adopt a solution. Whether or not you can seamlessly step into your client's process, that's the key to success.
Moreover, in an ever-changing market, it may be wise not to put all your eggs in one basket. Invest in multiple translation memory systems if that is what is needed to cover your customer base. It will be money well spent.