What is your definition of "toughest"?
# or rounds through it before it no longer works? Durability of finish? 100% reliability? Longest period between cleanings?
"Tough" means something different to every individual.
Just what are you going to use the pistol for? Strictly range work and large quantities of cartridges through it? Hunting - all different weather conditions but fewer rounds? A person carry piece for combat conditions?
Everyone will have their own opinion of what one is the toughest based on their own definitions. My Smith & Wesson M & P revolver could be defined as "tough". It's been going since 1952 - the year I was born. It still fires, is tight, accurate and dependable. But "tough"? Probably not if exposed to constant dirt and rain.
Striker fired versus hammer fired? Again . . . a "personal thing". I've owned many guns over the last 50 + years - more revolvers than semi-autos but I am not unfamiliar with semi-autos. Currently, I just have a SR9 and recently bought a Smith Shield - both striker fired. They both go "bang" when the trigger is pulled. Ask the next guy and he'll tell you that both are a piece of junk and the only one to get is a Glock . . or a 1911 platform . . or a Sig . . or a Kimber.
A person can run a "torture test" on any handgun and eventually, it will fail for one reason or another . . . and every tests performed by different individuals will be just that . . different.
I could take either my SR9 or Shield, throw it under the track of a bulldozer and if it shoots after that, I could pronounce it "tough" . . . but is it realistic since that is not "normal usage"?
I think you will also get a variety of answers based on the age and experiences of those responding. I have to believe that the majority of the respondents here are younger based on the number of "Block" replies. (And I'm not anti-Glock) But ask somebody who served in WWII and the answer would be much different. It would probably be the 1911 or 1911A1 - it served through all types of weather conditions it was subjected to including the sub-zero temperatures of winter combat in Europe as well as the hot, humid and wet conditions of combat service in the South Pacific.
In the end . . "toughness" is in the eye of the beholder. If you are looking for a striker fired 9mm . . . research them, look at them, rent them and shoot them at a range . . then make up your mind as to what "you" want . . . not what somebody tells you that you "want" or which is the "best" and the "toughest". No two people's needs are the same.