Three papers came out on new technique at almost the same time. What order do I cite? Three papers on a new technique came out at almost the same time. They are all similar and introduce a new method that I use in my research by providing a range of examples of that technique. 

Below are the dates the journals record it as received, accepted, first available online, and then the year of the official citation.

 Paper#  Received     Accepted     Available    Citation Yr.
 P1      2011-11-29   2012-06-21   2012-08-11   2012
 P2      2011-12-12   2012-11-01   2012-11-08   2013
 P3      2012-01-09   2012-08-30   2012-09-05   2012



By order received: P1, P2, P3
By order accepted: P1, P3, P2
By citation year:  (P1 P3), P2


Q: Should I cite all of them? I assume so. In which case, which order? 

I would like to cite all three, since all are in reputable journals and their submission dates were so close that I assume all three did independent work and are deserving of a proper citation. I am not sure what order to cite them in.
This could be a very delicate diplomatic issue. There might be three groups arguing over the paternity of the original idea. I strongly suggest citing all three.

As for the order, first of all check the journal guidelines. In my field, typically citations are numbered in alphabetical order in the bibliography; if it's the same in yours, then I suggest you to cite them ordered by their citation number (thus alphabetically), i.e., put them in the same bracketed list [a,b,c], with a&lt;b&lt;c.

Ordering the references like this is a good habit to adopt exactly because of these attribution issues.