Crossing from the Kruger park into Mozambique via Mapai is a beautiful trip if the Limpopo river is not flowing fast or in flood. We tried to do this trip about 5 years ago in December ( peak rain season in SA ) and after crossing the Pafuri border post ( probably one of the most organized and cleanest border post I have ever visited) we traveled towards Mapai to cross the Limpopo. However we had to turn back as the river was impossible to cross. We went back to Pafuri border post and crossed into SA again and then drove down to Giriyondo border post, which is as good and clean and organized as the Pafuri border, and looks more like a lodge than a border post, we crossed into the Moz side of the game reserve ( only ever saw a jackal ). The sand road is not bad to drive on, but when you get out of the game reserve and onto the tar road, it is TERRIBLE !!! The potholes are everywhere. I did this trip twice ( last trip was about 3 years back ) and the road conditions were still just as bad.
I cannot say if the Mapai route had better road conditions, but the little bit we did was very good. I will never drive from Giriyondo to Xai Xai again unless someone says that the road has been repaired.
I would suggest a crazy trip like the one we did a few years back ( we did this alone - my wife and 2 kids and myself ). We drove from JHB to Pongola and up the Jozini mountain road ( awesome views ) and up to Kosi Bay border post. Then its beach sand driving up to Ponta du Ouro. Sleep over there, and then drive up towards Ponta Malangane and stop for a cold beer, then drive up towards Ponta Mamoli. This trip from the Kosi Bay border to near Ponta Mamoli will be the best driving you will have done in many many years. I have been there more times than I have fingers and toes, and every time I drive there I feel like a little child in a candy store !!
From there you drive up to Maputo ( 80% sand road, 20% tar road, well sort of tar road.....
) towards the ferry. Catch the ferry, it is a wonderful and interesting experience in true African tradition. Don't stress with this part, but just go with the way things work. Go get a cold beer from the bar inside the ferry and enjoy the time. What we did the last time we were there was to spoil ourselves by driving to the Southern Sun Hotel to spoil ourselves. The Southern Suns hotel is right on the beach front. It was a bit expensive ( from a SA Rands point of view ), but felt fantastic to arrive all dusty and rugged and walk into a fancy hotel with the porters almost too scared to touch your bags because of all the dust ......
).They were VERY friendly and accommodating, and we felt like kings for the evening and next morning. From there we drove back to SA via the Komatipoort border post and back home.
If you wish to travel further, you can travel from Maputo up to Xai-Xai and even further up to Inhambane, and even further up to Vilanculos. From there you can drive west to Zimbabwe and do a trip all the way west towards Victoria Falls and and then cross into Zambia and east to the ferry into Botswana and then back down south to any of the border posts that take you into SA again.