Get the tools you need for achieving the level of quality the customer requires. Develop tools in-house or look to open-source or commercial tools for a solution.
Test design is more important than the tool you select. Choose a tool that allows you to develop tests according to the test architecture you're using.
You need more than test tools to deliver quality software. Source-code control, defect tracking, and build tools, among other things, are vital.
Experiment with different tools and approaches. Try a tool or technique for more than one iteration before deciding whether to continue using it.
Look for the easy tool, the simplest tool possible, the tool the team is most comfortable with. This minimizes the training costs and improves chances for the tool's quick and painless adoption.