There are of course caveats. Check out the Aegean Miles&More forum for more info. If you're planning on flying 50K+ qualifying miles per year on Star Alliance then United is the better (best?) program. You'll get access to UA lounges when traveling to/from Canada and MLLs domestically.

I was suggesting it primarily for the "I plan to fly the lowest fare always" case. Then, I'd suggest crediting AA, DL, AS, KL, AF, LA, CX, AM, BA, EK, KE, QF flights to Alaska Airlines Mileage Plan (no fuel surcharges, 1-way awards at 1/2 round trip). Any Star Alliance travel to United if you'll make 50K+, but if not, maintain an A3*G for priority perks.

That's what I have started recommending to my friends. It seems to make a lot of sense.