I'm sorry Caramela, I've never used EQP for Relaxed Hair. Only the Creme Conditioning one (which is a great poo). When I first joined LHCF there were tons of threads about both of these shampoos. That's how I started using it.
I haven't used the EQP CCP in months so I'll answer based on memory. The EQPCC is very, very moisturizing without leaving your hair feeling coated. I've never heard anyone say that their hair had buildup after using it. The CON often leaves people with the coated/buildup feeling. I don't experience that with the CON though.
If I stopped using CON, it's a no brainer that I would go back to the EQP because it works, it's cheap and easily accessible.
ETA: The EQP line is one of those where people either really love it or really hate it. I think it's a great line for the price.