We have decided to hire a 4x4 - simply it seemed more sensible to have a more robust vehicle for some of the dirt roads. We had a 4x4 in Namibia/Botswana a few years ago, and although roads there were generally pretty good, we did hit some deep sand in some of the NPs so it was more a necessity than a luxury.
Unfortunately it is not so easy to get a good 4x4 for hire in Uganda (Namibia had lots to offer, with fridges and roof tents etc) -
I did some internet searching - and found a few good reports on tripadvisor and such like for a company called Habari Car Rentals http://www.ugandarwandacarhire.com/ who offered a Mazda Levante for 3 weeks. Once I contacted them I found them very helpful and as they use a British bank account we could even transfer money to them without incurring massive banking charges. We have been corresponding with someone called Kizito who seems very keen to help - they have even searched the camping shops of Kampala to see if they could find a gas canister that would fit my little stove. (they couldn't so I'll be taking my petrol stove instead).
They have offered to buy a couple of camping chairs, which will certainly come in useful. They are going to deliver the car to our hotel in Entebbe.
We even managed to haggle a better price from them - so hire of vehicle, maximum insurance, and cross border fees/carnets - US$1750.00 (1325Euro or £1085.00)