We recommend staying at the Lemala Ewanjan , which is a small personalised camp in the Seronera Valley (the middle of the Serengeti). Listen for the animal sounds at night, from your tent.
To plan your perfect Serengeti Safari (1) first decide what you want to see and how many nights you want to go for, then (2) decide when you want to go and (3) contact all the reputable Arusha-based tour operators asking them to quote for you, and negotiate prices and (4) book the flights to Kilimanjaro Airport yourself.
Wildebeest Migration (this has a major impact on when you go)
Lake Manyara (hippos, monkeys, tree climbing lions, flamingos and other varieties of birdlife)
Serengeti National Park (endless plains)
Tarangire National Park (multitude of baobab trees and its tree-climbing lions)
Ngorongoro Crater (monkeys, elephants, flamingos in the lake area and open savannah where the lions hunt)
If you use a travel agent in your country they'll subcontract to a local party and want to add a bit of profit for themselves, so it's usually cheapest to book directly with a travel agent based in Arusha, and book your flights yourself (it's also usually easier to make changes to your itinerary if you've booked directly). Contact several Tanzanian travel agents and compare their prices. Be prepared to negotiate for a better price. Check whether:
they will meet you at Kilimanjaro Airport and drop you off there
the vehicle is a 4x4 and you have exclusive use of it
the driver is English speaking
George Mavroudis Safaris : firstname.lastname@example.org , ph +255 784 290 100
92 Haile Selassie Road, Arusha
A major decision impacting timing is whether you want to see the wildebeest migration. The migration is ongoing, as the beasts move as they please and depends on rainfall; but broadly speaking one can expect them to be crossing the Grumeti River in June and the Mara River in August. The Mara River represents the migration's biggest obstacle and watching panic & confusion of the frantic crossing can be quite spectacular.
Expect to pay more if you travel on the 24th, 25th, 26th or 31st December; 1st January; Good Friday to Easter Monday.
Rainfall occurs mostly from March to May, and October to November.
Typically, when safari tours stop at shops the prices are increased by anything from 3 to 4 times the usual price! The driver stopping there will also probably get a commission on your spend at the shop!