If you'd tell us more about what you're doing, it would help a lot. It's tough to recommend one over the other if we have no idea what you're planning on doing with it.
That said, I've worked with both Final Cut Pro and Final Cut Express, and in my experience FCE can do 95% of what you need. It will do all your basic editing, transitions, filters, etc. It will do basic text effects. About the only thing it will not do, IIRC, are some of the advanced cinematic effects that people working with actual film conversions would need. It is a very powerful piece of software for the average - semi-pro users.
The biggest difference, imo, is the supporting software bundled with Final Cut Studio. Motion is a fantastic program for creating animated titles, very cool transitions, and more. Color offers colour correction facilities well beyond what is included within FCP. And Soundtrack is a powerful music mixing program. I've never used LiveType myself, but glancing at it seems neat. And all these programs integrate flawlessly with Final Cut.
So, my suggestion given what you've told us is simple: if you need to do editing and little more, then go with Express. It will handle all of your editing tasks with ease. But if you need advanced functions, or the facilities offered by Motion, Color, or Soundtrack, then get Final Cut Studio.
