The S&W 645 is by far the best of the ones I've tried, including H&K, CZ97 and S&W. But, then, I have long fingers and need a large grip and long trigger to grip distance. HTH
Walt
In my opinion, the best double action in .45 ACP is the SIG P220. Nothing else quite comes close to it in accuracy, ergonomics and shooting comfort. Your mileage may, of course, vary.