Are there specific cities of regions you want to see? Landmarks you want to hit?
It's a huge country, so if you're time limited, I'd go with flying. If you've got a bit more time, maybe look up a train trip or two, but that can be super expensive. Buses are okay if you want a cheap way of traveling, but it takes a long time. Driving will take about the same length of time as a bus, but it'll get boring and tiresome driving long stretches.
I hope that helped! (If I misunderstood your question, please let me know and I'll give you a better answer)
Have fun! almost 3 years ago