Here is the basics on the characters with brief summaries on their drive, how they shoot and how to unlock them.
Notes: Drives, and Shot Trajectory for all characters but Metal Mario, and how to unlock all characters but Maple, Donkey Kong, Bowser, and Metal Mario come for the Mario Golf Instruction Booklet.
"Slight" refers to a fade or draw of 1 bar, "Medium" refers to a fade or draw of 2 bars, and "Sharp" refers to a fade or draw of 3 bars.
Plum: Drive: 208 Shot trajectory: Low and Straight How to Unlock: Playable from the start. Summary: Plum is the shortest driving character in the whole game, but her low trajectory and short drive also results in fast turnovers in stroke play.
Charlie: Drive: 210 Shot Trajectory: Low with a Slight Fade How to Unlock: Playable from the Start. Summary: Charlie drives short with his slight fade being extremely hard to correct through spin.
Peach: Drive: 212 Shot Trajectory: High and Straight How to Unlock: Playable from the Start. Summary: Peach is the best of the characters playable from the start with a high and straight shot, and fast character animations. She is used for Ring Shot%, Bowser% up until Yoshi, and 100% and All Birdie Badges runs for Courses 1 through 3.
Baby Mario: Drive: 215 Shot Trajectory: High with a Slight Draw How to Unlock: Playable from the Start. Summary: Baby Mario is probably the worst character in the game with long character animations for all but Par shots, a high and short drive, and a slight draw that is extremely hard to correct through spin.
Luigi: Drive: 220 Shot Trajectory: Low with a Medium Fade How to Unlock: Get Character Mode. Summary: Luigi is a mediocre also ran with a short drive, and his medium fade is hard to correct through spin.
Yoshi: Drive: 230 Shot Trajectory: Standard Straight How to Unlock: Get Character Mode. Summary: Yoshi is the most neutral character in the entire game making him extremely easy and consistent to use. Yoshi is also the only character that has a medium shot height, and is smack in the middle of every stat. Yoshi is used for Bowser% from Sonny till Harry.
Sonny: Drive: 240 Shot Trajectory: High with a Medium Draw How to Unlock: Get Character Mode. Summary: Sonny is a pretty mediocre character with a medium draw that is hard to correct through spin.
Wario: Drive: 250 Shot Trajectory: Extremely Low and Sharp Fade How to Unlock: Get Character Mode. Summary: Wario has the lowest shot in the game, and while his sharp fade is easy to correct through spin, his animations are extremely slow.
Harry: Drive: 260 Shot Trajectory: High with a Medium Draw How to Unlock: Get Character Mode. Summary: Harry has a medium draw that is hard to correct through spin, but he drives decently far, and is not a bad character. He used in Bowser% for Mario, and sometimes even Bowser.
Mario: Drive: 270 Shot Trajectory: High and Sharp Draw How to Unlock: Get Character Mode. Summary: Mario drives high and far, with a sharp draw that can be easily corrected through spin. Mario is used in Bowser% for Bowser often.
Maple: Drive: 245 Shot Trajectory: High and Straight How to Unlock: Collect 50 of the 108 Birdie Badges. Summary: Maple is the longest driving character with a straight shot, and is used in 100% and All Birdie Badge Runs for courses 4 through 6.
Donkey Kong Drive: 275 Shot Trajectory: Low and Sharp Fade How to Unlock: Clear 30 out of the 36 Ring Shot Holes. Summary: Donkey Kong is the farthest driving character with a fade as well as for one that does not draw. He can be unlocked extremely early in the 100% run if you do Ring Shot% first, and is excellent for clearing the last six Ring Shot Holes, collecting all the Birdie Badges, and Get Character Mode when he is third farthest driving character, and the second fastest character overall. On the Japanese NTSC version of the game that does not have Metal Mario in it, it is faster in the 100% JP run to unlock DK as fast as possible. It is also an easier and more reliable route for the 100% Run for the USA NTSC and EU PAL versions. Getting all the birdie badges with just Peach and Maple alone to unlock Metal Mario can get extremely dicey and slow quick. Making DK still an excellent option for the 100% Run when he still out drives all but Bowser and Metal Mario.
Bowser: Drive: 280 Shot Trajectory: Extremely High and Sharp Draw How To Unlock: Get Character Mode Summary: Bowser is the second farthest driving character in the game after Metal Mario, and the farthest driving character in the Japanese NTSC version that does not have Metal Mario. He shoots the highest, with the sharpest curve of any character in the game. Even his SW does not shoot straight unlike every other character. Despite being the second farthest driving character in the game, he is actually slower overall than Donkey Kong and Mario due to his extremely high and sharp shots.
Metal Mario: Drive: 285 Shot Trajectory: High and Sharp Draw How To Unlock: Collect all 108 Birdie Badges (USA NTSC and EU PAL Versions Only) Summary: Metal Mario is the longest driving and fastest character by a wide margin. His extreme spin from extremely high to low paired with his driving distance allows him to plow through everything with ease in every category he is usable in. However, you can only unlock him in the USA NTSC and EU PAL versions as he is not in the Japanese NTSC version at all.