A good side rail will be pretty solid. They're my favorite option. Since the scope stays attached to the rail, and you remove the whole rail from the mount, you can take it off and on to use the iron sights without having to re-zero the scope.

The problem is that there are so many variations of AKs that the mount itself isn't always sized right, and some of the crappier rails can be kind of wobbly. If everything is up to spec, though, they're great.

I'd stay away from dust cover rails, though, they always seem to be wobbly.