Right now my favorite caliber to play with (note I did not say anything about real world usefulness) is my 500 S&W magnum Hi-Viz.
For mild, indoor range friendly, target loads I use a 350gr Berry's plated flat nose over 13gr. of Trail Boss. Very mild subsonic load that is easy on the hands and ears. I can even shoot this one one handed!! Extremely accurate if you hold high to compensate for low velocity.
On the other hand when I need to defend myself from a the roving packs of Tyrannosaurs that plague southern Minnesota I stick a heavy bullet on top of a max charge of Lil'Gun from Hogdon's website load data. I've used 500gr Hornady (great bullet but expensive), 350 & 440 gr CPB hardcast (another great bullet but still kind of pricey and very slight barrel leading, and my current favorite: Remington 385gr core locked hollowpoint over 41 gr Lil'Gun for a muzzle velocity of about 1850 fps. This generates a dinosaur crushing 2925 ft-lbs of energy!!!!.
The full metal jacket keeps the barrel very clean, the high velocity make the bullet extraordinarily accurate over long ranges, and I can get a 100 count bag of these at Cabela's for about the cost of 50 count from the other brands!!!
I swear when I light off one of these big boys it makes my voice deeper and grows more hair on my chest.
There is just nothing more satisfying then stepping up to the line with this obscenely large monster and having crap fall off the shooting bench because of the shockwave. I always hear someone look up and say "Holy Sh*t - What the hell was that!!!"
You big bore power junkies know what I'm talking about right??