AA is probably the easiest to reach lifetime status, as all the miles count toward the status(brokerage accounts, credit cards, hotels, flowers, IDine, etc...etc...)not as some other airlines that only count actual flying miles. So whoever you choose, make sure that all the miles count. It's not easy to reach 1M(lifetime Gold) or 2M(lifetime Platinum) just by flying. Flying to Europe will give you about 5K miles each way, so even if you flew 2 times a month, you would only get about 20K per month. Ofcourse there is status bonus once you reach that, but at best with the above scenario you would still only get 40K. So, you could see how having all the other options helps you to reach your goal.
Good Luck!