I stay at both LM and LRM fairly regularly. Plat recognition in both is generally good.
If the price is similar, then LRM is IMO an easy choice. Some floors have been recently renovated so ask for one of these. As plat a renovated suite would be the first choice. If not available I would take a renovated standard room over an old suite but that is just personal preference.
Lounge wise, LM has a dedicated lounge. Happy hour from 7-9. Limited food option (2 hot + 2 cold item IIRC). LRM uses part of the main hotel lobby, but has a better selection of both hot and cold and some dessert items.
Both in a similar location - I marginally prefer LRM as access to the corniche is easier (great for a morning run/stroll), however no direct beach access. If beach is important then consider LM.