The closer they make it to the DS version, the better. I HATE the NGC and Wii versions because they don't reward you for good racing. If you are ahead, you are going to get pummeled to death with last place getting blue shells and lightning bolts. I don't mind the items themselves, but there needs to be balance. I feel like I spend 2/3rd of every race catching up and 1/3 of the time just spinning out from unavoidable items hitting me. Add in the course hazards and it just becomes pure un-fun for me.
You know, if they had some more standard-type courses with very few pitfalls, I think the NGC and Wii versions could have been a lot more fun. Instead you have to find this unfriendly balance between knowing the track by heart to not crash into anything and still maintaining enough speed to win while being hit by too many items.
That brings me to another thought. Because of the item systems, I hate using the heavy class racers. In the SNES version, they were kinda your advance class, where if you could control them, they were leagues better than the lightweights. But woe be you if you messed up at all. In the new MKs, there is no hope for avoiding being hit because you just can't avoid blue shells. With their slow acceleration, you may as well as stick with lighter karts because it won't be long before you get hit again and your acceleration is the only thing that is going to keep you in the lead.
Lastly, I want to see ALL tracks in one MK for once. It's not like they are running low on storage space theses days. Maybe not for the 3DS, but it would have made me a little happier for the Wii version if I had that choice.