Yes, any calibre that is nominally known as "243 XXX". So unfortunately you can't get a 6mm Remington even though it uses 243" bullets! Nor could you get a 240 Weatherby even though it too uses .243" bullets.
As to comparing 243 Winchester vs 243 WSSM I would say go with the widely available, easy to find and easy to sell 243 Winchester. You will have a choice from a Parker-Hale to a CZ-BRNO to a Remington to a Sako etc., etc.
In a conventional medium action rifle I really just can't see the point of the 243 WSSM when whatever advantage may give in a true SHORT ACTION isn't going to occur and at the expense of one less magazine capacity.
That said I also can't see what advantage the 243 Winchester offers over 6mm Remington in a true MAUSER action as used by Parker Hale.
I'd stick with the 243 Winchester. Quite simply so many people use it you will get recipes galore for loading (or dozens of factory ammunition variants) and dies etc cheaply from the UK or even from USA eBay.