ORIGINAL: Nord QC Bouman
243 is just a necked down 30'06 - so I would say the 308 - just speaking chambers. The game you are shooting does not need this type of round. I would look at a 222 or 223 - or even a 410 that you could also shoot a 25 slug and deer hunt if you want. Both the 243 and 308 are also great deer rounds. Reloading both will save alot of $$ if you like to knock off a few boxeson a Saturday.
Looks like you are best off buying 1 of each - just to be sure and have what you need.
Ummmm... The .243 is a necked down .308, not a necked down .30-06.
Other cartridges that are necked down from the .308 are the 7mm-08 and the .260 Win. Cartridges necked up from the .308 include the .338 Federal and .358 Win. Cartridges necked down from the .30-06 include the .25-06, the .270 Win, and the .280 Rem. Necked up from the .30-06 include the .338-06 and the .35 Whelen.
What the heck isa .410 with a "25 slug"?
To the original poster, for the uses you've listed, the .243 Win. is probably a slightly better round than the .308 Win. The .243 is a great round for any type of small game, from varmints up to and including Whitetail Deer.