Liwonde National Park is Malawi's best for Wildlife.   It is located on the Shire River - a tribuitatary of the Zambezi - and as a result is rather long a thin.  You can drive your own vehicle into the park, but you're limited to the main road (in the wet season this is often impassable) and a couple of small detours.  There is a luxury camp in the Park - "Muvu" (Muvu is Chichewa for Hippo) which although it seems expensive at about $90 per night for a tent, the quality of the tents, and the fact that the price includes three excelent meals, two game activities - usually a morning boat trip on the Shire and a game drive which starts in daylight and after a "sundowner" on the river becomes a night drive - means that it's pretty good value.  However, during the rainy season you have to add another $40 for the boat transfer to and from the camp.  Muvu also has shalets for $100 per night and the really plush Muvu Wilderness lodge (I think that's what its called) which is $150 or $200 per night I think - the extra gives you an even better   "Tent" with en-suite showers, toilets, etc.

Animal-wise you're guarenteed to see hippos and crocodiles.  Seeing them like this (out of the water) is easier when the river is lower and more of the sand banks are above the water.  But you can also see plenty of elephant, impala water buck, and baboons.  Less common are sable, kudu and bushbuck and the bird life, being on a river, is also plentiful.  Cats are more difficult, there are often rumours of lion, but usually if they're seen they are at the far eastern end of the park where none of the game drives get to - they come in from Mozambique.   Leopards exist and can be spotted on the night drives.