When it comes to evaluating prospects, the most important tools are hitting ability and the fastball. It's hard for a position player to have much impact if he doesn't have enough bat to make a difference, and most of the game's best pitchers build a foundation off their heater -- not just velocity but also life and command.

It's no coincidence that the top prospect in the 2021 Draft, California high school shortstop Marcelo Mayer, is also the best hitter. Or that the top pitching prospect, Vanderbilt right-hander Jack Leiter, owns the best fastball package available. They're both well-rounded players -- Mayer is also the best defender in this year's class, while Leiter has one of the best curveballs -- but it's their bat and fastball that could make them the first two players selected.

In our annual breakdown of the Draft's best tools in 10 categories, six of the superlatives belong to five players ranked in the top eight on MLB Pipeline's new Draft Top 250 Prospects list. Only players on the Top 250 were considered.

Best hitter: Marcelo Mayer, SS, Eastlake HS (Chula Vista, Calif.)
Like Adrián González, another Eastlake product who went No. 1 overall in the 2000 Draft, Mayer has a pure left-handed swing and outstanding bat-to-ball skills. He also manages the strike zone well, possesses plus raw power and draws some offensive comparisons to Corey Seager.

Also in the discussion: Colton Cowser, OF, Sam Houston; Peyton Stovall, 2B, Haughton (La.) HS; Sal Frelick, OF, Boston College.

Best power: Brady House, SS, Winder-Barrow HS (Winder, Ga.)
House is built to hit for power from the right side of the plate and could be a more athletic version of Joey Gallo. He's 6-foot-3 and 210 pounds, loaded with bat speed and strength and can do damage against good velocity and quality breaking balls.

Also in the discussion: Jud Fabian, OF, Florida; Joshua Baez, OF, Dexter Southfield HS (Brookline, Mass.); Niko Kavadas, 1B, Notre Dame.

Fastest runner: Seth Stephenson, SS, Temple (Texas) JC
A quick-twitch athlete, Stephenson earns top-of-the-scale grades for his speed from some evaluators. He uses his quickness to get on base and create havoc once he does, batting .383/.442/.674 with 31 steals in 35 attempts in 51 games this spring.

Also in the discussion: Benny Montgomery, OF, Red Land HS (Lewisberry, Pa.); Justice Thompson, OF, North Carolina; Sal Frelick, OF, Boston College.

Strongest arm: Henry Davis, C, Louisville
It's Davis' offensive prowess that makes him a lock to be the first college position player drafted in July, perhaps No. 1 overall by the Pirates. But his highest-graded tool is his plus-plus arm strength, which he enhances with quick footwork and fine accuracy on his throws. He threw out 46 percent of basestealers this spring.

Also in the discussion: Joshua Baez, OF, Dexter Southfield HS (Brookline, Mass.); Spencer Schwellenbach, RHP/SS, Nebraska; Bubba Chandler, RHP/SS, North Oconee HS (Bogart, Ga.).

Best defender: Marcelo Mayer, SS, Eastlake HS (Chula Vista, Calif.)
Far from a one-dimensional player, Mayer is also the best defender available and elicits defensive comparisons to three-time Gold Glover Brandon Crawford. He has all the physical tools to make all the plays at shortstop -- quick hands and feet, strong arm -- as well as an excellent internal clock.

Also in the discussion: Edwin Arroyo, SS, Central Pointe Christian Academy (Kissimmee, Fla.); Jose Torres, SS, North Carolina State; Justice Thompson, OF, North Carolina.

Best fastball: Jack Leiter, RHP, Vanderbilt
Proof that there's much more to a fastball than sheer velocity, Leiter's heater sits at 92-95 mph and can reach the upper 90s, but it stands out more with its riding action and induced vertical break that allow him to throw it by hitters in the strike zone. An American League assistant scouting director calls it one of the best fastballs he's come across in any Draft and it's the main reason why Leiter tops NCAA Division I in strikeouts (156 in 96 innings) heading into the College World Series.

Also in the discussion: Ryan Cusick, RHP, Wake Forest; Sam Bachman, RHP, Miami (Ohio); Chase Petty, RHP, Mainland Regional HS (Linwood, N.J.).

Best curveball: Seth Lonsway, LHP, Ohio State
Lonsway rode his curveball to 98 strikeouts in 68 innings this spring, generating an impressive 52 percent swing-and-miss rate. He uses a high arm slot to stay on top of his bender, which combines low-80s power and depth, reminding some scouts of Barry Zito's trademark curve.

Also in the discussion: Levi David, RHP, Northwestern State; Mack Anglin, RHP, Clemson; Jack Leiter, RHP, Vanderbilt.

Best slider: Jackson Jobe, RHP, Heritage Hall HS (Oklahoma City)
Jobe's slider is almost legendary in scouting circles, with multiple evaluators grading it as an 80 on the 20-80 scale.

Easily the top prep pitching prospect in this year's class -- he also has a fastball and changeup that can be well above-average offerings at their best -- he unleashes two-plane sliders with low-80s velocity and spin rates in excess of 3000 rpm, and he also has the ability to locate them where he wants.

Also in the discussion: Kumar Rocker, RHP, Vanderbilt; Sam Bachman, RHP, Miami (Ohio); Mack Anglin, RHP, Clemson.

Best changeup: Jordan Wicks, LHP, Kansas State
Wicks ranks as the consensus best left-hander available in large part because of his changeup, a low-80s weapon with tumble and depth. He sells his well above-average changeup with deceptive arm speed, uses it against both left-handers and right-handers and commands it well.

Also in the discussion: Jackson Jobe, RHP, Heritage Hall HS (Oklahoma City); Jaden Hill, RHP, Louisiana State; Kevin Abel, RHP, Oregon State.

Best control: Michael McGreevy, RHP, UC Santa Barbara
McGreevy doesn't possess a true plus pitch but his precision control of four offerings could land him in the first round. He ranked second in NCAA Division I this spring in both K/BB ratio (115/11 in 101 2/3 innings) and walk rate (1.0 per nine innings).

Also in the discussion: Braden Olthoff, RHP, Tulane; Gunnar Hoglund, RHP, Mississippi; Dylan Dodd, LHP, Southeast Missouri State.