It all depends on what you're doing. If you fish the major lakes with good ramps 2wd is fine. I've seen people pull 17ft. Lunds with a Crown Victoria and pull it out of Lake Cumberland. (it was interesting, but it worked) If you are putting into places where the ramps aren't built well, are gravel, or if you fish the river and have to get into it you will want a 4x4.

I fish the river and I go places on other adventures that require a 4x4, but if I didn't have too I wouldn't have one. It's just one more piece of equipment to break on you.