I agree with Giddens but not Walker
You agree that Giddens offense isn't good enough, but disagree with Walkers defense isn't? I think that probably has more to do with your preference for Walker over Giddens, than about who's actually more ready. If we're picking between good offense, and good defense for this team you've got to take the Good defense.
We need the rookies to be able to defend if they want minutes, not score. If they're able to defend they can play on the floor without being a liablity, the offense will come. Scoring is the easiest part of basketball, the hard stuff is rebounding, defending, and making the right plays. I would say that Giddens is ahead of Walker in those departments, and he's still the better scorer (according to d-league numbers).
I doubt either of the two Rookies knows our offensive or defensive schemes well enough to warrant playing time off of that alone. With that said, I do think both of the Rookies are ready for real minutes in the NBA, but not extended minutes. On this team giving rookies a huge amount of minutes wouldn't be smart. What we lack is consistency from the bench and we're not going to get it from the rookies.
If for some odd reason we were to give one of the two a chance, I think Giddens would be the wiser choice. You pick Walker if you feel his size, and height will make that much of a difference over Giddens. You pick Giddens for his defense, and rebounding the points and scoring opportunities will come. According to Doc neither is ready, but if I had to pick one of the two i'd go with Giddens.
...then again this is all probably just based on my preference for Giddens over Walker.