Ones that are not strong enough if you get really stuck if I remember right.......
If you are going to play in the rough stuff, then get a couple made / added that'll take 4.75T shackles, you know it makes sense, the ZJ is a heavy beast to start off with.
For light weight work, you may get away with 2.25 (Or whatever the smaller one is) but I would not go below this and I would not use these "Off Road" with a ZJ (I wouldn't use them with a Wrangler at 2/3 the weight).