If you ever plan on useing it for bigger critters go with the 243. I personally would go with the 223. there are so many factory loads for it and lots of bullet choices. There is nothing wrong with the 204 but generally they have a slow twist barrel and prefer bullets under 40gr. Depending on the manufactured the 223 comes in twist from 1 in 7 up to 1 in 12 with some exceptions. The slower twist (1 in 12) work great for the 40 to 50 gr bullets and the faster (1 in 9, 8, 7) are better with bullets from 55gr up to 70gr. This is not the rule and there will be odd ones in the mix. but you can buy 223 off any walmart shelf but 204 is a bit harder to find.
Good luck with the one you choose. I have a couple of bushmaster varminters and looking at a new X-bolt varminter in 308. the semi-auto is great when you have 3 or 4 coyotes come running in