The Captivate does indeed behave in a similar fashion to the Vibrant, when it comes to both good and bad points. Beyond reviewing them, I've owned them both, and loved the display and Hummingbird CPU + GPU, but there are TouchWiz bugs and occasional lag.
Personally, I'd go with the Inspire. It's a really lovely phone and HTC Sense is hard to beat. It's also a newer model, and that's always a plus. The only drawbacks with the Inspire are mediocre battery life that's worse than the Vibrant and Captivate's and the lack of Super AMOLED.