The answer to this one is purely personal desire, you are either going to really want a bore-gun or you're not!

If you really want one, then you better get it or the regret will probably eat you up eventually!

The .577 is the more practical choice IMHO, as it is a more versatile hunting calibre today than it has ever been (read what I really think here!

). But if you are hunting largish quarry at shortish ranges, a properly set up 12-bore would give-up nothing to the light .577 IMO. ...and both are simply marvellous vintage Brit nostalgia!