You need to take into consideration the Westin Lagunamar is probably 30 years newer compared to the Westin Cancun! I think the original Westin has done an excellent job in keeping that hotel tidy etc.,

I have stayed at both places and on a personal level I would stay at the original Westin in heartbeat. The RBC rooms are nice enough and very quiet; the beach is fantastic and again quiet at the end of the strip; bus fares?? seriously I think it's like $1.50 and picks you up right outside the hotel - I think it is fun taking the bus and experiencing the culture rather than hopping a cab everywhere; super close to the airport and usually excellent prices.

As for the Lagunamar, I had given it a shot once and immediately was turned off from first impressions. Very impersonal and a much bigger property - several things I could list but simply was not impressed. Yes the rooms are newer and it is in a great location but that did not sway my judgement.