Another reason not to choose LH is their mileage expiration policy. Most airline miles now expire after a period of account inactivity, but in many cases a FF account can be 'kept alive' in some fairly easy way (a small online purchase is an old favourite). Miles & More doesn't allow most customers to do that. Overall, I think it's fair to say that M&M is great for some very frequent LH flyers based in Europe, but not so good for anyone else.

If I was fairly sure I'd be visiting N America then I'd definitely consider United.