I'd go for a firm
landing in x-wind conditions. I think that landing soft is always a good thing but in case I have a severe x-wind then I'd rather not make it any harder on myself. (But instead make a firmer landing)
I have made at least 15 x-wind landings and it doesn't get easier if the wind is blowing at a none stable rate. Drawing conclusion from this then I believe that it is indeed better to land firm.