Best Ugandan safari parks are Queen Elizabeth National Park and Murchison Falls National Park.
Murchison is in the north of the country which is a bit more dangerous on paper but the park itself is amazing (and is the only one which has giraffes in the country iirc) and it’s a really nice luxurious resort, very honeymoon friendly for sure.
Queen Elizabeth is a bit less luxurious but the park is amazing again and it’s also close enough to Bwindi if you wanted to do a gorilla trek or something as well (there’s also a chimpanzee trek near QE which was dead good as well)
Not done any safari in Tanzania but you can feasibly do it there and get yourself over to Zanzibar for a lovely bit of traditional resort honeymooning, we went to this place last year which was bloody lovely:
http://www.hideawaynungwi.com/en/
I’ve not done it but apparently Kenya is the absolute creme de la creme for Safari though.
Gissa shout for any tips or recommendations for anything non-safari related in Uganda as well if you want.