Don't go by the Clock speed. The Barton is faster. 333FSB, 512K L2 Cache, Cooler and on and on. I own the 2400+ and it's a nice CPU but the Barton is better. AT the time I did not have PC2700 or higher ram and was on a budget so I bought the 2400+ but would have gotten the barton if I could have afforded the RAM at the time.
There are tests here on Anandtech and other sites that will show the barton 2500 faster in all benchmarks. If you have PC2700 or higher ram GO BARTON! You won't be disapointed!