Just entering this to help anyone here who hasnt already beaten the Career mode on Midnight Club 3.

First off, at the beginning of the game the best car to choose overall: This really depends on your personal style of driving, but in my opinion the best to start out with is the Dodge Neon SRT4, since it has the best stats and will get you through until you win the Lexus IS300, the best D-class Tuner.

The most important thing to do through out the whole game is beat Racers (Like Vanessa of San Diego, Vito of Atlanta, and Ceasar of Detroit, and Tokyo Challenge races (purple races) in Tokyo) and Clubs (Unbeatable Street Racers, Big Playas, and By Invitation Only). Normal street races (red flares) are good for money, but wont help you progress, though they can be good practice. The last way to progress is through doing tournaments (example: City Tournament (San Diego). Prize: IS300)

The racers you will face through the game are: In San Diego- Vanessa, Bishop, Carlos, Phil, and Vanessa [rematch].
In Atlanta- Roy, Dre, Vito, Cheng, Naomi, Lamont, and Roy [rematch]
In Detroit- Roy [rematch 2, since defeating him twice wasnt enough for him], Leo, Spider, Ceasar, Kioshi, Ceasar [rematch], and Angel, though you will meet several of these racers again for the U.S. Championship series.
In Tokyo- Tokyo doesnt have any street racers. All progression in Tokyo is made by doing Tokyo Challenge races (purple flares) so just do any random race. Each 5 or so a tournament will unlock.

Clubs you must face are: Unbeatable Street Racers (Tuners), Luxury Roller Car Club (Luxury Sedans), American Royalty Car Club (Muscle Cars), Chopper of America Bike Club (Choppers), Big Playas (SUV/Trucks), Origional Riders (Sport Bikes) and By Invitation Only (Exotics). Beating the first 3 or so races of each club will unlock a special move for that car class (Zone for Tuners, Exotics, and Sport Bikes, Roar for Muscle Cars and Choppers, and Agro for SUV/Trucks and Luxury Sedans). In Tokyo each of these clubs has a tournament that can be unlocked by doing Tokyo Challenge races.

As you progress you may notice a Tournament open up. Tournaments can be used to make money, and win cars (which you can sell for more money if you like):

City Tournament (San Diego, 3 races)- $5,000 and IS300 (Tuner)

Balboa Park Tournament (San Diego, 3 races)- $4,500 and Chrystler 300C "DUB Edition" (Luxury Sedan)

Stage Tournament (San Diego, 4 races)- $5,000 and 1957 Chevrolet Bel Air (Muscle Car)

DUB Tournament (Atlanta, 4 races)- $9,000 and Cadillac Escalade EXT "DUB Edition" (Truck)

Hotlanta Tournament (Atlanta, 3 races)- $10,000 and 2004 Ducati SS1000 (Sport Bike)

Bad Boyz Tournament (Detroit, 4 races)- $20,000 and 1949 Chevrolet Fleetline (Muscle Car)

DUB Tournament 2 (San Diego, 3 races)- $12,000 and Mercedes-Benz SL55 AMG "DUB Edition" (Luxury Sedan)

Detroit City Tournament (Detroit, 3 races)- $20,000 and Cadillac Cien (Exotic)

U.S. Championship Series (San Diego, Atlanta, Detroit, 14 races)- money from individual parts and Lamborghini Murcielago (Exotic)

Finish all these parts and you will have finished the main Career mode, and be the U.S. Champ.

I havent yet finished Tokyo, but am at 51% and working on it still.

Cars won from Tokyo Tournaments:
*= Price of car in Buy menu. All stats stock unless otherwise noted.

Chevrolet Cobalt SS (Class D Tuner)- $21,995*
Acceleration: 14.3
Top Speed: 37.5
Handling: 36

Dodge '05 Magnum RT (Class D Luxury Sedan)- $32,070*
Acceleration: 12.8
Top Speed: 30.6
Handling; 34.0

Nissan Sport Concept (Class C Tuner)- $28,000*
Acceleration: 19.9
Top Speed: 43.2
Handling: 34.5
Tuned-
Acceleration: 34.5
Top Speed: 43.2
Handling: 57.5

HotMatch Chingon (Class C Chopper)- $113,000*
Acceleration: 40.2
Top Speed: 42.5
Handling: 51.2
Tuned-
Acceleration: 53.7
Top Speed: 64.5
Handling: 51.2

Dodge '06 Charger SRT8 (Class B Tuner)- $35,995*
Acceleration: 24.7
Top Speed: 55.2
Handling: 49

Gemballa '98 F355 (Ferrari F355) (Class A Exotic)- $200,000*
Acceleration: 76.9
Top Speed: 94.3
Handling: 80.6

Final tip: When your doing a tough race don't give up and start over at the first sign of things looking bad. If you screw up and land in last place on your first try, don't worry, and use that try to learn the route and the best short cuts for that race. The first time you do a race use that time around to learn the route, and then use the second try as your winning one; though you should try to win on the first time round anyways, and the best thing you can do on MC3: DONT GIVE UP, EVER.

Personal MC3 info (Stat Screen; Career stats):
Total wins: 315
Tournaments won: 14
Skill Rating: 92
Racers beaten: 26
Vehichles unlocked: 88 as of Sept. 13th

For all of those who are wondering about some of the higher up A class cars new, and otherwise to Midnight Club, I'm submitting the stats and info for the Cadillac Cien, Chrysler ME 4-12, Gemballa 98 F355, Lamborghini Murcielago, and what I know about a last car I havent won yet:

Cadillac Cien: Cost- Prize for Detroit City Tournament (Autocross races- 3 parts. Best won with McLaren F1)
Stats:
Acceleration- 62
Top Speed- 88.5
Handling- 69.5

Chrysler ME 4-12: Cost- Prize for By Invitation Only race 16 (Last race with BIO. I won with Cien, though there may be more suitable options)
Stats:
Acceleration- 91.6
Top Speed- 95.6
Handling- 91.6

Gemballa 98 F355: Cost- Prize for Tokyo By Invitation Only tournament (Best car for winning is ME 4-12 in my opinion)
Stats:
Acceleration- 76.9
Top Speed- 94.3
Handling- 80.6

Lamborghini Murcielago: Prize for U.S. Championship series (San Diego mechanic mentions it every time you get out on the street after unlocking U.S. Champ series. Have yet to win it myself, thought have done 2 races with Skyline and 2 with ME 4-12. I suggest the ME for this tournament)
Stats:
Acceleration- ?
Top Speed- ?
Handling- ?

Pagani Zonda C 12 S: Cost- Prize for Imperial Tournament (Final tournament in Tokyo. Saw car on screen and fell in love, so I looked up all I could online. Have yet to actually win it. Should be won with ME 4-12)
Stats:
Acceleration- ?
Top Speed- ?
Handling- ?

Ok all you have to do is buy the gemballa yes I no when you see the price you will possibly pass out but sell all the cars you have until you have enough money then buy it.Race the tournaments and it will be like racing in a sports car you will win easily and get the H3 (Hummer 3) then sell your gemballa then you have all the money back to buy all your well deserved cars and also the prize money of the races to pimp them up easy or what.