I would personally take a 3" ccw gun over a 2" or 2.5" ccw gun. However, this is based on using 357mag ammunition.
The difference isn't actually that great, but the extra 1" -1.5" of barrel does help boost velocity by 50-100fps, IIRC. It will also aid due to longer sight radius. So it helps a little to get some extra "oomph" out of the caliber and will lend for more accurate pointing.
In reality though, for some reason 3" barrel guns have become quite the "fad", and S&W examples are approaching unreasonable prices & Colt examples might as well be crafted of gold.
So if being able to choose a 3" was a possibility, I would have one, but with such a price hike to get one, I have no problem sticking with a 2.5" and just losing maybe 50fps velocity.
I guess it depends on how desperate you are for those precious extra fps. In most cases, I don't think the difference will matter that much.