For a range gun, a dot sight is OK. For defense, you might want to rethink it.
The only advantage of a dot sight on a HD gun is for illumination of the aiming point--which can be accomplished by using night sights. Now, if you still want to go for it, the best pistol dot sight on the market is the Ultra-Dot. Yes, they're a bit pricey--over $100.00. But, they're durable--I have Ultra-Dots mounted on my competition guns, including my wadcutter gun--it's a slide mount, meaning that when the slide cycles, it cycles, too. So far, about 2000 rounds through the gun, with the scope mounted--no problems, still dead-on zeroed, too.