Amboseli in Kenya is one of the best places to see elephants as you have Mt. Kilimanjaro in the background. Tarangire National Park in Tanzania is also famous for its elephants but make sure you go in the right season of they might have moved to the Ngorongoro Highlands.
The country with the most elephants is Botswana and Chobe National Park, in the north-east (near to Victoria Falls), has the biggest herds of elephants in the world, some in the 100's.
For forest elephants its much harder as they live mainly in central and western Africa which are harder and more expensive to get to. You can get more advice on a specialist safari holiday website like realafrica.co.uk