Either, really.
Consider that at least for now you can obtain normal capacity Mini 14 factory mags, and that for the time being 7.62x39 ammo is hard to find aside from corrosive-primer Yugo (not a dealbreaker, but a factor nonetheless). If you're thinking about a 5.45x39 AK, then factor in obtaining a good supply of ammo for it now (while it's affordable), plus mags which are more expensive than for its bigger brother. Do not buy a Century 5.45x39 weapon without first confirming that the barrel is in fact built for the 5.45 and not the 5.56. Six months ago I would have leaned in favor of the AK. Now? The Mini 14!
Another consideration for some is that the Mini in its stock configuration does not look as "evil" as the AK. It will not attract as much attention in some circumstances. The same is true of an unmodified Saiga. That may or may not matter. If you want a pistol grip and folding stock for the Mini 14, there are several good ones to choose from for well under $100 each, Butler Creek being one of them.