He has an LJ so it's the 4.0L engine.
The 6-speed is geared lower than the 5-speed is so while 4.56 is the usual recommendation for 33" tires and 5-speed transmission, it's kind of a toss-up between 4.10 and 4.56 when you have the 6-speed.
If your TJ is primarily a street & highway Jeep, I'd probably go 4.10. If you spend a lot of time offroad & really want the best offroad gearing, 4.56 would be the way to go. The rpms with 4.56 would be a little high on the highway but not so high that it'd be a problem at all. Personally, I'd go 4.56 even with the 6-speed due to my TJ being mostly an offroad Jeep, but that 6-speed would probably make most people feel better with 4.10 gearing on the highway if their Jeep is also a daily or near daily driver.