First you have a 4x4 vehicle depending on how much wear is on the old tires you may have to buy 4 new tires. What happens it the old tires will be smaller diameter and it will cause 4x4 to be engaged all the time and will cause damage.
Here is a recent thread on this
2007 xlt 4wd auto sounds engaged
On to tires if everything checks out ok with the old tires and you only buy two tires then you should stick with the same tires as the old. If you have different tread patterns the car may not handle the way it should (particularly in rain and snow).
For specific tires thats up to you. Good brands are Michelin(they are not cheap), Yokohama, General tire, dunlap, pirelli (again they are not cheap), and continental. Most tires are pretty good as long as they are a known brand. I run falken tires as my summers and they are great in rain but are a little noisier. For winters I have dunlap tires and they are awsome.