I'm thinking the big twist will be that neither is lying. Christian said that Grant had a very off look in his eyes one moment, then was normal again the next. Sounds like programming to me. Ward thinks he wasn't brainwashed, but I'm willing to bet he was all along, and some of his memories are altered to accommodate it.
However, if it comes down to a case of one is lying and the other isn't, Christian is the liar. As previously stated, we've seen the memories through Grant's eyes, so whatever he says happened as a kid, he believes it's wholly true. Something tells me if that's the way this goes, Christian is HYDRA and is the one who arranged for them to get their hands on Grant to begin with. The angle of forcing Grant to bully their younger brother may have been a means of testing the conditioning.
Whatever the case, something about Christian's story just screams HYDRA programming. So for now, I'm going with the theory that Ward was brainwashed, just much younger than he would expect, which is why he believes he wasn't. I just know I was happy to finally see the big escape. Hate to say it guys, but I'm rooting for Ward right now. Been waiting for him to get out of that box all season.
Edit: I also got to thinking, and they dropped another heavy hint of brainwashing in this episode besides Christian's story. At the beginning when Simmons was commenting that Ward wakes at the same time every morning like clockwork, yet had no clock to wake him. I get that a person can train themselves to wake up at certain times, but that seems a bit too precise to me. It screams "programming" in my opinion. Just thought I'd toss that out there too.