Agree with everyone so far...I've played with both for 20 years. My main player has been my Schon SL 17. I went from a Joss J15 (stolen) to a custom Gary Medlin (several years) to a Joss N11, then to the Schon (16 years and counting).
Joss J15 (circa 1989): Solid cue, ivory ferrels gave it a softer touch...only had it for 2 months.
Joss N11: Solid hit, a little stiffer/harder than the J15 due to micarta ferrels and the straight grain forearm. It was my break cue for 15 years once I got my Schon, and a real monster. Now it's my son's player.
GEM (Gary Medlin) custom: Szamboti tribute, 59 1/2 inches with 12.5 mm ferrels. Whippy, took getting used to...but then I loved it. Seemed to almost play by itself, just putting the right English on the cue ball without any thought from me.
Schon SL 17 (now STL 17): Fell in love with it the first stroke I took. Stiff hit, but the feedback and feel of it was very nice. Comletely subjective, but the cue just felt more "substantial" and solid than any of the others. The Schon shafts are just slightly better than Joss...tighter pores, nicer grains, I think they're probably better aged or higher grade maple. I still use Joss shafts on my Schon occassionally as back ups with no problem--they're fine, just not quite as nice.
You can't go wrong with any Joss or Schon...it comes down to price and appearance preferences, really. But having had both for a long time, I prefer Schon.