What of lager or stout beer is healthier?

You have to define healthy. There are alcohol calories, carb calories and the effects of alcohol to consider. The two kinds of beer are actually ale and lager, not stout and lager. However since you mention stout, which is a kind of ale, I will say that Guinness draft (either on tap or in the can, but not the Extra Stout in the bottle) has in the past been recommended by doctors in England because it's fairly low in alcohol and calories for a beer with that much flavor. Of course, that's England. They see things differently.

If you're not into flavor, you could say that those bland super-light beers, 55, 64, etc, are less unhealthy than other beers. I wouldn't say that any beer is the same as consuming, say, whole-bran cereal. Life just isn't that perfect.