I worked at the south rim of the Canyon for a year in the 80s and that's where I met DH. He had worked there for five years at the time. I would second a helicopter tour. Also a bus tour of the West Rim/Hermit's Rest from the Grand Canyon , although in February it is also open to cars now I believe. The visitors center should be able to refer you to one of the transportation desks, where you can purchase tickets. We took the train once from Williams Arizona to the GC, but I wouldn't really recommend it. It doesn't offer any views of the canyon, and unless you are a big train fan, I wouldn't spend my time doing it. If you exit via the east rim, you will end up on the Navajo reservation. There used to be a great restaurant there in a little wide spot on the road called Cameron, at the intersection of 64 and 89. It was the Cameron Trading Post and they had wonderful mutton stew or Navajo Tacos. I'm not sure if it's still there or not.
I would recommend catching sunset and sunrise over the Canyon, if possible. Breathtaking. Also, the restaurant at El Tovar Hotel is very nice, although expensive, and offers views of the canyon. We used to enjoy going there for breakfast, since that was more affordable.
If you are driving up from Tuscon to the Grand Canyon, you may be going through Sedona and Oak Creek Canyon. That is one of the most beautiful places on earth to me, and well worth getting off of the interstate to travel through there. We went back for a visit 3 years ago, and Sedona was definitely more "commercial" than when we lived there, but Sedona and Oak Creek Canyon were both still beautiful. You see a lot of jeep tours for this area, but I don't ever remember taking one, so I can't say anything about those good or bad.