I think the first thing to do is ask the opportunity question.
Drew is behind Fred Taylor, who, by all accounts is running well. There's the injury issue, but aside from that, I think it would be close to impossible for Drew to win the starting job.
Turner is in the same boat. No injury = no upside.
Gado is in a different situation. He could wind up winning the job in Houston, and we've seen him running in NFL games. The note of caution here is that he was reported throughout the summer ot have a hard time adjusting to the zone blocking scheme, and I suspect that GB got rid of him precisely for that reason. Still, given the dearth of talent at RB in Houston, he has a real shot.
Washington is somewhere in the middle. On the one hand, there is no RB who MUST get touches - the starting job is wide open. Washington is undersized, but he's built thick - a Jones-Drew clone. We haven't really seen enough on the field to evaluate him - he had a couple of nice plays where he showed speed and elusiveness, but we really haven't seen him all that much. I think that given the presence of Barlow and Houston, two big backs who haven't run out of chances yet, Washington is probably not going to take the starting job anyime soon. However, I'd rather have him on my roster than pray for an injury to LT.
I guess I like him about as much as Drew.