Toad

History:

Toad is known as Consigliere to Princess Peach Toadstool in the Mushroom Kingdom. As such, he wields immense political power but as a good nature Shroomhead is known for being nigh incorruptible. Still, as one of the few High-Ranking Mushroom People in a Royal Family otherwise full of Minorities he wields considerable influence. Some of his acquisitions include the Kingdom's large Highway System as well as a large Factory that produces Item Boxes for the Races themselves. Toad has thus been able to parlay the success of the Cups into an industry in of itself. Outside of these properties in Transportation and Industry Toad has extended a deep political influence over more of the Road System of the Kingdom, including the byways of Mushroom City from the glamourous Entertainment District to some of the Seedier Underpass Neighborhoods.

Super:

In SMK Toad's stats are radically different than they would be in later games. He's ranked along with Koopa Troopa as The Small Guys and only has an outstanding Handling Stat. His Weight is low and Top Speed and Acceleration Medium. There is no course he is explicitly associated with but in general he's considered a good driver, mostly due to his Handling. With the Rival System opponents will finish in the order Peach, DK Jr, Mario, Yoshi, Luigi, Koopa, then Bowser. This may hint at some antagonism between Servant and Master.

64:

Toad was ridiculous in MK 64. This began his era of being universally the Best Racer in the Game. While he gets knocked around easily by the bigger drivers and handles a bit looser and slipperier, he makes up for all by having the best Acceleration and Top Speed. It's insane. 64 also introduced Toad's Turnpike, which has no real reference to the Shroom himself but provided the template for many more Traffic-addled courses to come, usually all with some Toad reference. His Kart is blue.

Super Circuit:

Super Circuit finally differentiated slightly between the Lightweights. While Toad and Peach still had similar stats, including very high Top Speed and very low weight, Yoshi had a bit less speed in exchange for a bit more weight. Toad is still awesome here though and his acceleration is Top Notch. He has no track explicitly associated with him.

Double Dash:

Toad by himself in Double Dash is nothing special. Every light character in Double Dash is identical save for their Special Items. It's the Toad Kart that really shines though. It has the 4th Fastest Acceleration in the game and at a Top Speed of 56 mph. While plenty of Karts are faster, it also has some of the Best Shocks, which gives it great power against the many hilly courses and big jumps. While its handling is only average and it's the 19th lightest Kart out of 21 total it also has one of the best Offroad Speeds in the game. The positives far outweigh the negatives here.

The major drawback to using Toad in particular though is his item. The Golden Mushroom seems like an excellent one, it provides an infinite amount of Mushroom Boosts in a short span of time. However if you're in a High Position in the Race you'll never see it, so it doesn't offer much help. There are also dangerous courses like Wario Colosseum and Rainbow Road which offer enough tight turns that boosting through will leave you rammed into a wall instead of at the head of the pack. It's excellent for the Mushroom and Flower Cups but not much else.

DS:

DS is the first game since 64 where Toad isn't absolutely awesome. The only major difference between characters in this game is weight and Toad is one of the lightest, adding about 0.2 to the weight of all his Vehicles. All of his Kart Options offer very high Acceleration and decent Handling and Drift but their Speed is awful. His fastest, the Mushmellow tops off at a measly 4.3 in exchange for a paltry 3.3 Item ranking. This is still probably his best Kart, count on using it to get ahead and racing well instead of acquiring the good Items. Here's a chart:

He has Staff Ghosts on Shroom Ridge in 2:05:123 as well as the Double Dash Retro Courses Baby Park in 0:50:920  and Mushroom Bridge in 1:30:600. For all of these he uses the Mushmellow. It's interesting that they had to fit him into Baby Park because he's the most innocent, baby-like character in the game.

Wii:

Each Wii character may choose between six Karts and six Bikes in his or her Size Class, each with widely varying statistics. In addition each Driver adds certain bonuses to each Vehicle. Toad again has acceleration as his staple, adding a whopping 6-pts to any Karts' Acceleration Stat. He also adds 6-pts to Drift speed, which basically means that even if he's driving pretty slowly he'll never really lose speed, and if he does he reclaims it very fast. Here are all the Vehicle Stats specific to Toad:

As you can see, some of these stats get real good. It's hard to resist using either the Cheep Charger or the Quacker, as ridiculous as these vehicles are. He also makes the Blue Falcon and Bullet Bike pretty usable, but let's face it, at this point you haven't chosen a Light Racer for Speed. I think acceleration is much more useful in Grand Prix Mode when you're constantly being assaulted with all kinds of dangerous Items, while in Time Trial Mode it is all about speed. Thus Toad has a single Staff Ghost Track, his eponymous Factory. The Normal Staff time is 02:22.480 in the Bubble Bike and the Expert is 02:05.593 in the Blue Falcon. These are also probably the two vehicles he can be most associated with, if any.