A question like this is always going to come up with the personal (and fan-boy) favorites. Yeah, there's the AI/TRG guys that are always coming around trumpeting the toughness of their particular systems, and the DTA guys spouting off about the versatility and compactness of theirs. I'm wondering why nobody said the AI PRS though if they want true versatility and toughness...
Me though? I have my favorite. My M40A1. Nope, it's not the hardest hitting being held to .308. Yep, the trigger and bolt release can give you issues and they're far from versatile. Sure, the wire reticle isn't the best and I've had them break before and hell, I don't even have a bipod or DBM either. But quite frankly they're tough, simple, accurate and it flat works for me. It's my good old friend with volumes of memories in my head of good times, even if they were shitty at the time, but good times nonetheless.
I'm glad having just one isn't the case. I'm an American and buying out of "wants" versus only needs is how we roll, so I'll also keep my multitudes of other rifles, pistols and shotguns, each with their own place and purpose, even if that purpose is simply having good times banging steel and busting clays.