Of the five global US airlines three offer one form of lifetime status and two offer lifetime lounge memberships, I've always thought it funny that with one brief exception, i.e. AA for one quarter in 2005, no airline has offered both in recent past.
Of the lifetime programs AA has the most generous-because of the ability to earn status based on miles from all sources. And, although I'm almost always a CO or WN fan, recently AA does seem to be a little better at redeeming miles. The big downside to earning lifetime status on AA or UA: having to have earned that many miles without flying CO.