I got quite obsessed about barrel length at one point with my rimfires... bullberry barrel works publish some great data on optimum barrel lenghts, but basically if you're bunny bashing I wouldn't worry too much as the most important thing is that you have a decent threading and crowning job done! Then put a decent moderator on it (I like the MAE mini-t)
My .22 is 15 inches (CZ542) - I had a 14" volquartzen custom barrel on a 10/22 that was just as accurate if not more so! - the shorter it is the louder it will be, but basically for a pointable rifle that's not a pain in the 4x4 I'd reccomend between 14-16".
In the pic mine is the one closest (15") and my mates is the one furthest (21") - I'm seen him do a bunny at 200 yds plus, but realistically these shots are so rare (usually within 100yds) that I much prefer being able to shoot out a vehicle and laugh at him trying to wiggle is gun out of the window!