Hi Sunaholic,
I've not stayed at either hotel but have passed them both. Their locations are totally different - Le Blanc is on the main strip in Cancun so plenty of bars, restaurants and shopping plazas within walking distance or a short bus ride. The EDR is situated on the Riviera Maya south of Cancun off the main Cancun-Tulum highway. The Riviera Maya has some fabulous beachfront hotels that are resort-based and walks are restricted usually to the beach. All the hotels offer organised trips and tours and it is easy to catch a collectivo or bus into Playa del Carmen or Cancun.
We stayed at the Iberostar Maya for our wedding last October and had a fantastic time. Have heard nothing but good reports on the EDR - especially cassitas section - but don't know much about Le Blanc (other than it comes out the most expensive on most holidays searches for Cancun!).
Hope you have a great time when you decide where to you!
Cazz