In terms of quality, capacity, and flexibility I think the Saiga wins hands down. I don't have any experience with the Saiga .223, but I've read good reports here and on the Saiga forum I have in my signature.
I have owned a Saiga 308 converted to the traditional style, and have nothing but good things to say about the brand.
I don't personally care for the lack of detachable magazine or capacity of the SKS, but many like them.
As for AK, well, a SAIGA is an AK. It is easily converted back to its traditional configuration. AK is a nebulous term that encompasses everything from entry-level AK-style rifles like Century products, to mid-level rifles like Vector and Lancaster Consulting, to high-end rifles like Converted Saigas, Arsenals, Tromix creations, and builds from companies like Krebs.
In terms of flexibility, I prefer a Saiga over a SKS. In terms of AKs, I prefer the Saiga over entry-level and mid-level AKs. In terms of accuracy, I prefer a Saiga over just about any AK. And dollar for dollar, a Saiga is a great buy-- probably more value than getting a high-end AK.
But if you get a Saiga already professionally converted, you'll pay a premium price-- but then again it is then right up there with the high-end AKs.
-- John