What is the right place to acknowledge another (simultaneous) paper with the same result?
Τhe sections of Introduction and Related Work of a paper serve the purpose to inform the reader exactly about related results/attempts/techniques etc in order to put their result in the correct perspective. As such, the "other" result should be mentioned and cited there, preferably with a direct comparison of the possibly different techniques involved. Anything else, could be potentially misleading and/or suspicious and should be avoided.