That really depends on what you are aiming to do. My favorite is the Modified Association saddles as they are the most comfortable and secure for me, but not everyone would like how they feel. Is there any particular type of saddle that you have sat in and really liked?
As for the horse being comfortable, nobody can guarantee that it will fit your horse properly, but I've been using mine on quite a few different horses and none of them have shown any inkling of soreness or discomfort.