I would say it depends on what deer you might shoot in the future and whether or not you want two rifles.
There are 2 schools of thought here:
1. Get a .243 and have a good all round rifle, albeit one that's a little on the lighter side for the larger deer but great if you're only ever going to shoot fox and small deer
2. Get a .223 for fox and then you have good reason to apply for a heavier calibre for deer later eg. .30-06 or whatever takes your fancy.
My mate chose the latter route simply because .223 opened up the possibility of a heavier calibre whereas with .243 being deer legal on all species, there's a bit more to justify when applying for a heavier calibre if you already have a deer legal rifle such as a .243. It shouldn't be hard if you can justify the need for a heavier calibre, but you will need to justify the need as to why you need a heavier calibre than the deer legal one you already have, which may depend on the terrain of your permission and the typical shooting distances involved, whereas with .223, you just mention that you need to shoot deer that aren't legal on .223 with no further justification required. With the latter, provided the land is safe for that calibre, you're away!
That said, there's little point paying out for eg. a .30-06 if you're going to target small species at close range as it will just cost a lot more in ammo and cause safety issues with shots passing through.
Not sure that helps necessarily in making a decision, but it does give a few factors to consider.
Edited by Alsone, 09 July 2014 - 08:15 am.