DTA SRS Deployment System with .308, .338LM & .510 Whisper barrels. :-)
I always get a chuckle out of threads that are almost akin to asking "you can choose only one 'do it all' drill bit, what would it be?" The answer depends on a number of factors including what size hole you want to drill, what material you are drilling, how deep you want to drill, do you want a through hole or not, etc, etc, etc. Similar factors apply to gun calibers and I suggest there is no such thing as one "do it all" caliber which is why so many different calibers exist in the first place. The reality of "one size fits all" often ends up being "one size fits none".