If you are really reading it on a Kindle, any complete works will be a navigation nightmare and likely difficult to read. I checked out the Oxford, which is at least reasonably authoritative and unlikely to contain errors found in other editions. There is a huge introductory section before the plays start so you will need to get to the table of contents and click on the right one to jump, and it is more than $15. There are some pretty excellent apps for iPad if you are using that.

Otherwise, I guess Oxford is ok but unless you are looking for a deal, if you don't want paper I think you would be better off getting individual plays for Kindle. You can find at least some editions of individual plays from the Folger Library on Kindle, for example, and those are excellent, although they will run you $5 - $6 each. Some Arden editions are available for Kindle, too, and those are even better, but more expensive.

If you don't need the accompanying essays, etc., and just want the play in a readable format from people who know what they are doing, there are some editions that look pretty good, like this one for Macbeth for only $0.99.