The only way of getting lounge access on US domestic flights is to have a non-UA *G card, so I'd say just go with SK, you'll make 24k points per R/T meaning you'll earn *G within 2 trips (45k is the threshold), and with 4 R/T you'll easily make Diamond (90k) which will allow you to gift a *G card to a friend or family member.

Redeeming on SK will also be cheap, since SK does not charge YQ on its own metal IIRC.