What working model FEA does everyone use

IMHO, MSC "Visual Nastran" (new name of "Working Model") and Cosmos are very similar programs. Both are very well integrated in SW and will do all the "standard" linear analysis without noticeable differences. I personally have a slight preference for MSC for reasons that I can detail, but maybe it's only because I used it more... If you're happy with your Working Model, upgrade to Visual Nastran, you won't be disappointed. You should be able to use WM on SW2003 or later, I can't see a reason why it wouldn't run (except that the motion module won't handle the new "mates"). Try and tell us.

You've said nothing about your analysis requirements.

I was pondering a switch to COSMOS. We consulted local FEA guru Vince Adams, who is well versed in COSMOS and MSC NASTRAN.
For our needs, COSMOS fell short. Of greatest concern was COSMOS' inability to do large displacement nonlinear (which we need). Also noted was that COSMOS can not combine multiple element types (i.e. plate + rigid + gap) in a single analysis. We're sticking with MSC.
We are fortunate to someone available like Vince Adams. He is in a position to make unbiased recommendations, as he is not directly affiliated with any single FEA software pushers. He is available for this type of consultaion and can be reached through Impact Engineering Solutions in Milwaukee, WI (USA).