We recommend North Serengeti for clients traveling between July to October and planning for 6 days or longer itineraries and to those who are okay with longer transfer times.
Huge herds of wildebeest and Zebras (the great migration) that gather here between July(anywhere between June 2nd half to Jly 1st half) to October are undoubedtly the biggest draw for this region. The experience of seeing mega herds is unlike any other wildlife sighting you might have during safari. If you are patient, with a bit of luck, you might see wildebeest herds crossing the Mara river and attacked by crocodiles.
There is more wildlife to be seen in North Serengeti apart from great migration but not as much in variety or numbers as you can find in Central Serengeti or other parks like Ngorongoro, Tarangire. So its not worth traveling all the way to North serengeti outside the migration season.
North Serengeti is quite far from Arusha and it takes about 11-12 hours to arrive by road. So we don't recommend North Serengeti in short itineraries, even during July to October season, unless you are planning to fly in and/or fly out from North Serengeti.
If your focus is primarily seeing big 5 or big cats only and not keen on seeing wildebeest herds, you can skip North Serengeti. Lastly, adding North Serengeti to your itinerary can make the tour expensive (compared to adding other parks) as Serengeti park fees is expensive and accommodations here are limited and charge higher than similar tier accommodations at other locations.