Pooner

Hi guys, I am new here and think I kind of like it. I have been searching through past posts and learning lots of useful info. I do have one question for the pros (all of you). I have a 04 supercab lariat, it comes with the 18 in rims stock. I am working on getting a leveling kit and new rims and tires. My question is I have been told by two different people that I have to keep my 18 inch rims on the lariat, and by a few that say I can go with a 17. I want to go with a 17, cheaper tire and a little smoother ride. So which is it? I have been looking for this everywhere and in the past forums threads but can't find it. Thanks in advance. My leveling kit should be showing up shortly. I hope it gives me a little more clearance for those rutted out two tracks. Thanks again.