I dislike the standard push-button magazine release on most pistols (Glock, S&W, etc). As one with small hands, I cannot reach the button with either my strong or support hand without significantly altering my grip on the pistol. When executing reloads, I've been taught to reach for the fresh mag with the support hand, after it's been secured, drop the magazine with the strong hand. This is tactically sound, but I can't do it without shifting the pistol in my hand. Under stress and/or with sweaty or bloody hands, this could cause me to drop the pistol, and at very least, I need to reestablish my grip once a new mag is in place.
I GREATLY prefer the ambidextrous lever style found on pistols such as the Walther P99 and the HK P30. With this style, I can use the lever using the middle finger on my strong hand without shifting the pistol at all. This can be done while the gun is on target, or after bringing it up into my "workspace" as in a tactical reload.
Also, the ambi-lever mag releases can be used identically regardless of your shooting hand. This is good when teaching support hand shooting tactics, as the same reload methods can be used.
I carry a Smith and Wesson M&P because I like almost everything about that gun, and I shoot it very well. But if I could change one thing, I would give it the ambi lever style mag release from the P99. I'm a right handed shooter, but I've actually switched push button on my M&P to a leftie style, just so I can push it with my strong hand middle finger. It's not as good as a lever, but it's better that change my grip entirely to make up for my stubby thumbs.