On/Off vs. Sleep Mode
I really don't think it matters. I put my MBP to sleep all the time because I like always opening it to exactly what I had open before. There are probably plenty of arguments that you can extend its lifespan by doing something or other, but unless there's a defect or you drop it in the pool, it's going to be obsolete long before it wears out.

Additionally, on flash-based Macs (Airs and Retina MBPs) running on battery power, the default setting is to go into standby after 70 minutes of sleep. Standby is essentially hibernation - the contents of RAM are saved to flash and the machine is powered off almost completely.