dear  Sougrati Belattar, Femlab is now called COMSOL. Having use besides Ansys and COLSOL also Abaqus, DEFORM a.s.o. I guess COMSOL is slightly easier, although the difference to my experience is not so big. However there are some other differences like the Marketing strategy: COMSOL provides a permanent licence with you are buying a temporary licence with Ansys. Having this in mind COMSOL is much cheaper when used over more than 1 year. It is also important to look for Support although I have no knowledge about the conditions and costs for Support with Ansys (for Abaqus you can hardly affort it).  

thanks dear Rüdiger Rentsch