I used Turbutax for many years, then switched to Taxcut for several years due to the Cdilla fiasco, and then switched back last year. A couple of observations:
1. Both are fine.
2. Taxcut had some annoying crashes and bugs, esp. in the CA state version. These were unfixable, and required tedious workarounds.
3. Turbotax might be a little more obvious to use.
4. I really like the PDF publishing ability of Turbotax. This lets you print a complete copy of all your tax documents to a PDF file for achival storage. Also, you can email it to any computer for printing.
5. Intuit learned from the Cdilla mistake, and fixed it.
6. Turbo tax is more expensive, usually.
7. Switching programs is a hassle as they don't pick up last years return info.
Conclusion: If you have been happy using one, stay with it. If you haven't used either, use Turbotax. If you are really cheap, use Taxcut or Taxact.