I like the showers in UA's Red Carpet Club, personally. That's always my first stop. Then, if I have more time, I saunter over the SEN lounge in B (often crowded) to see what kind of munchies they're serving.
The "quieter" SEN lounge in A is alllllll the way at the end of concourse, making it quite a hike! Pretty much the same deal as far as munchies, but better views IMO.
Yes, you can enter the RCC, SEN and LH Business lounges as a *G member. Whether your MP statement and boarding pass will be enough to get you past the LH matrons is perhaps another story.
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"There are those who travel, and those who travel well."