Will be going to kruger next year july/august. Normally I wouldn't really mind knowing already now where we will be going, but my SO wants to discuss, since it will probably be our second and last trip to South Africa for a little while

SO wants to get the most out of our Kruger experience, so we want to stay at nice campsites with great places for spotting wildlife, but where the roads aren't totally crowded.
Since we are not totally sure how long we will go and everything, I thought: why not ask this great forum for some advice?
So here I am, asking you guys for advice:
How long should we go to Kruger so that it will be both enjoyable (with nice sightings) and still not too long?
Where should we go? We like reptiles and mammals the most, although we both really enjoy (colorful) birds.
Last year (2014) we went to 4 different campsites in just 7 days and though it was a little too much, since we just flew in from the Netherlands.
So this year we want to stay a little longer at the places.
Last year we went from Malelane gate to Skukuza(not our favourite) the next day to Satara where we stayed 2 nights. After that we went to Balule (which we didn't like, because it is extremely small) and finally to Letaba, which we absolutely loved because of the river view.
What would you guys advice? Is Lower Sabie really that crowded in july and august?
Thanks in advance,
mattie010