All of them is a good answer but, since I'm a little limited on funds, I'll have to go SLOW, one at a time.
I do more paper punching than anything, and have a .308 & .270 in the X brands.
But really doesn't matter.
Deer and varmint are about all I hunt, thought about the 30-06 but didn't know how pleasant it would be to shoot alot.
with deer and varmints i would get one of these 25-06 would be good,30-30,45-70, 243, or 308 which is what i am looking at in the survivor but will add to that, if you handload 280 is a good one to have and i am sure i could think of more and i am sure there are some more custom stuff that this bunch could suggest. they are know what they are talking about more than i do.
You've already got the deer and varmints covered with the 243, so grab something that works well for one or the other, you don't need another cross over chambering. The 223 is inexpensive to shoot if you don't handload, if you do, then get it or the Hornet, or something bigger like a 280 or 30-06. All you have to do is figure out what chamberings you want, then decide which you want first!!
Tim makes a very good point here about selecting your next caliber. Personally, I'd go with a .223 bull barrel for paper, varmints, and a second predator caliber. Even though this caliber is readily available over the counter, it a great caliber to reload for. With a little work and patience, you can get a .223 Handi to shoot very small groups.
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