I think there might be several threads comparing the two if you try the search option...Both are great gigs...
I take it back - did a search of my own and couldn't find a thread asnwering your question...
I agree with Slice though, apply at both and if one hires you - you just won the powerball.
but let me ask you this - given a choice would you prefer to work for Atlas or for Polar...ooops, never mind