I think a lightweight, 16" barreled, AR15 in .223 topped with a 3-9x40 scope is about as good as it gets for me.
I like the idea of all the other cool calibers (.17 Rem, .204, 6x45, etc...) but as a non reloader I am stuck with factory ammo. Therefore, .223 gives me the most bang for my buck.
I'm left handed and prefer a semi auto for quick follow ups and multiple targets, hence the AR platform.
I think a 3-9x40 scope offers more than enough magnification while remaining light. I had a 4-16 on my AR and it was too much so I switched to a 1-4. The 1-4 is OK but I would like a little more magnification and I hate the reticle on the 1-4. I plan on adding a plane jane Leupold VX2 3-9x40 with a duplex reticle or possibly the 2.5-8.
Just my idea of the ultimate predator rifle, others will vary. Once you have one, you will want another, then another, and so it begins...