While I have not read it myself, "The Kaddish" by David de Sola Pool came highly recommended to me by a leading scholar in the study of Aramaic when I posed the same question to him a few years ago. (This question has reminded me that I am very far behind on my reading list.)
This scholar's response to my question at the time was, in a nutshell, that the former seems to be the most "correct". As an added bonus, part of my question to him was centered around the point that there is a Yod that, if my Babylonian Aramaic class in college taught me anything, ought to be a Lamed. He responded that it is written in Geonic Aramaic, which has some deviations from Babylonian Aramaic of other periods.
Unfortunately, without his consent to quote him and broadcast his opinion throughout the interwebs, I feel I must withhold the identity of this scholar from the broader audience. But if he recommended a book on the subject, I feel confident recommending it to the community.