7.62x39 has been imported for quite a bit longer than 5.45, so it would be fairly safe to assume that there is more in the country at this time. Magazines are similarly priced, so that's not really a factor.
5.45 bullets have a small air pocket in the nose to make the tip bend upon impact and start the bullet yawing ASAP. Other than that, I really have no experience with it, but I kick myself for not buying a Romanian AK-74 when I had the chance.