I'm one of those who owns both.
I've been playing RG5XX's since 87 or 88, my first being an RG550 desert sun yellow.
This past December I bought my first JS
, a JS1000BP. Very nice.
Then in February I decided I should take the plunge and get a Jem, I ended up getting a 7VWH, Also very nice.
The Jem is more comfortable to me, but thats probably just because of the familiarity after play RG's for 15 years.
But, the JS1000 is very nice too. It sounds great, it's very comfortable, and easy to play.
Between those two and my trusty Fender American Standard strat, I basically have an electric suitable for any situation.