I'm going to surprise myself here and go with Beckham. The lowest downside of the bunch is Aybar, but he's really nothing more than a fantasy replacement player. The ChiSox, I believe, aren't going to call up their stud and then take the job away from him, which really seems the only downside risk for him. He's not a not likely to be a fantasy stud, but he can give you very solid numbers in several stat cats, making him a bit of a poor man's A-Ram.
Aybar - consistent... but consistently worthless. Doesnt give you much, and may sink you with the average. Kennedy - playing well now, but beyond his historical stats. Also doesn't have a guaranteed starting position. But could get 3 pos eligibility. Harris - 3 positions, but nearly empty at bat filler. Beckham - hasn't played any MLB ball, no way you can call him a low risk guy
BUT given the compelete lack of UPside to most of your options, I dont think Beckham has much down side. My order would be Beckham, Kennedy, Aybar/Harris. But not really based on your low downside criteria.
So the reason I was asking is I have a trade that I am ready to pull the trigger on, and the other guy wants me to throw in Beckham for Kennedy, and my offense is easily the top in the league (Kennedy could get replaced by Aybar when he plays one more game at 2b, and Asdrubal Cabrera when he comes back).
How far a downgrade is it from Beckham to Kennedy for 1 week, Aybar for 2-3 weeks, Cabrera for the rest of the season?