I have both currently and they are both superb weapons.
Drawing on just my experience with both and no 'hard facts' here are my opinions:
Accuracy - I would suggest that the .223 is more accurate, and has longer effective range then the .30c. I shoot at 50yrd and 100yds only and use open sights typically. I have scoped my mini14 for the 100yd range where I havent the mounst on the carbine to do the same but on the 50yr ranges I had pretty good results and tighter groups with the mini14 than my carbine seems to be able to provide.
As for reliability - I think it is a bit of a toss up, both use a similar gas design, and their simplicity makes them very reliable. Both are well made. The carbine is battle tested and my 68 year old carbine is still working flawlessly. My Mini has a few thousand rounds through it with not a single issue.
Cost of ownership (initial) is also about the same, you can get rack grade carbines at Big5 sports for around 800 bucks, and the .223 ruger is also around 800 bucks. Parts are available for both, but the carbine parts can be pricey.
Long term ammo costs- I would give the nod to the .223 as you can get it at any sporting goods shop and it is often on sale, the .30 ammo is a bit harder to come buy and costs more per round.
Accessorizing- well the mini wins hands down in this area, but hey, if your looking at a vintage .30 carbine, I assume you like the steel and wood era rifles and wouldnt be looking for the 'zombie killer' looks and accessories, but if you are, there are some carbine stocks and accessories available, just not as many options as the mini has.
Bang for your buck on the "fun meter" - depends on how you shoot, if scopes and targets are your thing, the mini is the better choice, if just plinking is your intent, the carbine is a blast to shoot, has no recoil and is small so it can be easily shot by children or smaller women.
Cool factor - well, again, depends on your taste. I have been on the range with my restored 1943 SP carbine and had plenty of folks stop by to chat about it and in a day and age where the 'black rifle' is the most common thing on the range, wood and steel often stands out just because it's differnent.
Home Defense - well, neither is a good choice in my opinion. Shooting a rifle at HD ranges such as a hallway often will lead to over penetration so I would look elsewhere for a HD weapon.
SHTF - I would go with the mini as the .223 round is more plentiful, is a NATO standard, and would be easier to find in times of social disrupiton.