Just to add that A3 Gold can be thought of as relatively stingy, but at the same time is very easy to obtain and maintain.
Though I am based in Germany, I will never, ever go for M&M, since it is basically impossible to get the same perks with the amount of flying I do (most of my flights are within Europe, but I do have 3-4 trips to US/Asia every year). My boss is M&M silver, and I basically have more benefits than him even when flying LH. For example, I can check in at LH first class counters, which is a *huge* bonus when flying from a crappy airport like Tegel, while I get into the Senator lounges (+ a guest), while he's always forced to use the busier business lounges.