For me the choice is clear. If I was down to only keeping one rifle, I'd keep the .243.
The .243 (and/or 6mmRem) was my dual-purpose yote/deer rifle for a few years. Works great for either critter even with the same load (100gr SP).
Yeah I've hunted yotes with dad's .270 (and my .25-06) but they're not the best hide-hunting cartridges. But it's tops for whitetails and plenty good enough for elk too unless you're trying to take shots clear into the next county.
So...Keep em both and expand your ammo selection.
-75gr HP for prairie dogs
-100/105gr SP (or 90gr Barnes TSX/TTSX) for coyotes and whitetails
-130gr Barnes TSX for coyotes. (It works darn near like a FMJ...very little expansion on yotes. Two small holes in the hide, both easily stitchable.)
-130gr or 140gr for whitetails.
-140gr or 150gr for elk.
-150gr Barnes TSX or 160gr Nosler Partition if you really need a thumper for big deer (elk/moose/etc)
You can hold off on the .22-250 and .300Mag for a few years this way.