AK and Oyster Date are primarily the same size at 34mm. COSC is a dealer's bargaining chip at most, not yours. Dealers will tell u that this watch is COSC, so fetch higher. When you want to sell the watch, they dun give a damn about the COSC. In fact, the COSC is valid for only 5 years or less after the watch is sold from the AD, and that's it. IMO, just a certification to make the buyer pay more. We have seen from the bros who bought sub non dates that their watches run well within COSC tolerances.
Of course if u want a better resale value, it really depends on a good number of other factors, with the major ones being - e.g. How old is the watch? the model popular? Generally, the AK and the OysterDate do not fetch much in the pre-owned market if u were to read into the previous threads, so maybe u can up your budget by a thousand and get a datejust/exp1. From what I see, you've the new-Rolex-owner dilemma...dunno what to buy. Bottomline is.... u're already gonna spend a few grand on a watch. If you like a datejust, but because you wanna save a few dollars and end up getting an AK, u'd likely regret and be thinking of the datejust 1-2 weeks later. So, hold your horses and give yourself more options to decide what you really want, expose yourself to ALL rolex watches within a certain price range and take your time to decide.