I own a .410 and I know several gys who have the 12 gauges. I've only shot one of the .308s. They seem to be very reliable guns, good weight and decent ergonomics. If you're not looking for a tack driver, the Saiga is a good choice, especially for the money, when it comes to semi-308. I'd recommend the 16", but I'm partial to shorter barrels in almost every application. Even my 2 Loooooong range .308's have 20" barrels.
-RJP