I am an avid fan of the .243, but I use it as an allrounder.. Ie fox and deer. (Roe mainly)
I cant believe I'm actually saying this, but I would advise getting a bigger rifle than a .243 if you are setting your stall out for soley larger animals. The .243 will kill large deer with good shot placement, but if it were the mainstay of quarry.. Go bigger.
It doesn't cost anymore to run a .308, than a .243, That would be my choice. It that is too big for you, my next choice would 6.5 x 55mm. There is a plethora of calibres, but why go exotic when one of the mainstream calibres will do the job pe