They are very much peas in a pod however I would not expect much in the way of SB from Kendall on Oakland. They had 47 TEAM SB last year, only the Giants and Rockies ran less.
I was thinking Estrada might have some more upside being 'younger' but he's only a couple of years younger so I would just take whoever I thought would be the best pick in terms of draft location, which would be Estrada as I've not seen him ranked > Kendall in too many places.
There's not all that much dropoff for Estrada and if he's cheaper, I'd wait on him and grab Estrada. And, if you've waited until those two come around, there's some other guys not too far off like Michael Barrett lurking even a couple of rounds AFTER that.
On a related note, for some reason, RotoChamps projections have Estrada down for 18 HR from which I would have to conclude that they are smoking crack or something?