If you don't care about where the miles are credited, I'd go for UA Premier Silver.
*G and UA Silver are pretty much equivalent in most regards—you get most good stuff either way: a chance at E+, premium boarding and premium security lines. *G would get you into the crappy lounges at EWR, but would require splitting your family up at an inconvenient time. UA Silver gets you a chance at an upgrade to J, which for a CUN trip (a leisure destination) gives you a half-decent shot at getting you +1 upgraded (give it to the wife + kids: happy wife = happy life).