I'm not so wise, but I have been accused of enabling!

In my humble opinion, the .500 JRH is the most logical and practical of the various .50 cals. It fits in a "normal" sized gun, offers all the terminal performance one could want, and has a wide selection of bullet availability. Also, you can produce brass from .500 S&W brass with ease.

That said, I do like the .500 Linebaugh and the .500 Maximum a whole lot as well. I wouldn't waste my time with a .50 AE, but that's just me.

The best platform -- aside from a full-blown (read: expensive) custim, in my humble opinion, is the BFR. It is available in .500 JRH and they are accurate to a fault, typically, and reasonably priced.