I actually just picked up copies of Military in Scale and Model Military International. They're both pretty decent, and I would recommend both. If anything though, their format and styles are so similar that you'd almost swear they were the same mag.
AFV Modeller is amazing, but as others have said is quite expensive, and probably one of the harder modeling mags to find. Most people probably end up ordering it online.
Tamiya isn't bad, but it's loaded with ads, the articles are fairly lightweight, and the mag is obviously heavily skewed towards Tamiya products. And interesting read if your looking for a modeling mag to browse through rather than something that will teach you new techniques.
FSM is a great mag, but at times I feel the content is a little lightweight, and this is coming from a relatively inexperienced modeler. Still a decent read though. I wish they had multiple editions though that focused just on armour or vehicles, as I could care less about air and sea. They really need to get up to a full 12 issues a year though, as you can't be a respectable mag with less.