With 6" of lift you ought to be able to slam 35s under that thing *if* you wanted to. 285/75r18s are a 35x11.50. That's what I run on my Silverado.
If you want 33s, I am a huge fan of 285/75r16s. 33x11s. I run these on almost all my vehicles, including my two off road rigs. Very common and they are a great in-between size between street tire and off road tire.
Skinnier tires are generally better in every terrain except sand where floatation is necessary. For mud, snow, rain, etc, a narrower tire allows better traction because they sink thru the soft stuff down to hard pack.
Have you settled on a tread style and brand yet? I have run a lot of tires. I am a huge fan of Falken Wildpeak AT3Ws for a solid all terrain choice. Awesome tread life and great traction in everything I've thrown at them including mud (within reason, of course. Still an all terrain.) Very good in the snow especially. I've owned 3 sets now.
For a more aggressive tire, I have really liked the Dick Cepek Trail Country EXPs. Still a smoother ride and quieter than a mud tire, but more aggressive than an AT. Good hybrid.
For outright mud tires, there are a lot of options. I generally go with what's cheap that I like the look of. Making sure they have good siping is important for the rain and snow. Remember, in the snow you actually prefer the tires to pack in for better traction. If you deal with a lot of snow, mud tires are not your #1 option.