Travelling Nairobi to Masai Mara

I am visiting Nairobi for the first time in January and plan to drive to Masai Mara myself. I am just wondering where is the best place to go in the Mara? I'm unsure of where I'm heading other than toward Narok?

My budget wouldn't be huge and I am staying in Kenya for a total of 18 days so am looking for tips on accommodation I will be travelling with a friend of mine, I also plan to visit Tsavo National park. If anyone has any information in regards to hiring a car (preferably 4x4) it would be much appreciated.