Which area offers the best wildlife viewing?
Of course that is a bit subjective because I don't think anybody is doing or has done actual wildlife counts, but in general, I think you can normally see more wildlife in the north. There are several remote lodges in the south where you can see a lot, but many lodges in the north benefit from being near the Trasnpantaneira Highway, where you can see many animals from the road. Also, the north is close to the southern part of the Amazon basin, so you can either drive to some Amazon lodges on the fringe to get a taste of Amazon wildlife, or you can fly from Cuiaba to Alta Floresta to access the Cristalino Lodge in a wildlife-rich area, very popular with birders. So, you don't have to fly all the way up to Manaus to access the Amazon.
But for people who want to see jaguars, the north is definitely the place to go to, especially around Porto Jofre, but also in other remote areas. There is a new boat there offering jaguar cruises now.
Many of the lodges in the north can be easily accessed year round because the elevated Transpantaneira Highway, but the south doesn't have anything like that, so during high water season, it is difficult to reach some of the lodges, except by charter flight. Xaraes can be reached with the help of a ferry boat. Others can be reached by muddy roads.
Be careful when choosing packages because some of the lodges, particularly in the south, don't have English-speaking guides, so you have to pay extra to have one brought in.
What about flight connections to other cities? Well, neither Campo Grande or Cuiaba are great in that respect.