I like all cards but my favorite ones are:
Cities, Sights, Scenery, retro, Dancing pairs, Movie stars and Singers (like Elvis Presley,Marilyn Monroe, ......and many others), and more. Please write in Print. And please no religious motives. I'd like to receive a souvenir from your country with a postcard in an envelope.
But I will leave the choice to you.
And for Christmas, of course, Christmas postcard :D
Happy postcrossing :)