The amenity fee at the Ren makes the LAS Marriott a better option, since the MAR doesn't have any fees. MAR doesn't have an exec lounge but it offers free full buffet brekkie or order off the menu to Gold/Plats & all the rooms are suites. And the MAR staff are some of the friendliest in the the entire MAR family.
Given the Ren's extremely close proximity to the South Hall of the LVCC my guess is they'll keep the amenity fee because they know the biz travelers will pay/expense it.
Cheers.