Rancho, Rancho, and Rancho again.
Take it from someone (me) who has personally run Fox 2.0s, Bilstein 5100s, OME Nitrochargers, and Ranchos. The Rancho shocks ride the best of the bunch if you ask me.
The others are very good shocks, they're just meant for a much heavier vehicle for the TJ, and therefore they ride way too stiff for a lighter vehicle like the TJ (yes, the TJ may seem heavy, but compared to a truck it's not!).
For your 6" lift, you could run the
Rancho RS999062 rear shocks, along with the
Rancho RS999061 front shocks. Those shocks are both meant for 6" of lift, and they offer dampening adjustability, which can come in handy from time-to-time.
Since Rancho currently has their rebate going on, you'd get $50 back off your purchase by using their rebate form which you can find here:
http://www.gorancho.com/downloads/promotions/rancho_spring18_rebatepad_us.pdf
I hate to sound like a salesman for Rancho (because I'm not), but I am telling you, these shocks really ride amazing! the only way I would go with any of the others is if you prefer a much firmer / stiffer ride.
The Ranchos are going to ride much smoother. Not so soft that it feels sloppy, but soft enough that people who get in your Jeep will constantly comment on how good it rides for being a Jeep. They also perform excellent off-road.