As far as FFPs go, UA is more generous in most aspects than LH. As you are US-based it would make sense for you to stick with that, not least because of the credit card earning opportunities. But I would second Yoshi's point about upgrades...you won't get them with your travel pattern. You will need to fly a lot (like 100,000 miles per year) to qualify for certificates, or redeem miles earned plus payment.