DISCLAIMER: This is not a list of the "best" hitters in the Marlins minors, nor the ones with the highest potential. Rather, the prospects currently in the Marlins minor leagues with the best power tool currently. Also, players eligible for this list had to have finished the 2013 season in the Minors.
No other player on this list comes close to Colin Moran in terms of overall potential across all phases of the game. The 2013 first-round pick from the University of North Carolina is without a doubt one of the top three prospects in the Marlins minors, and some of that has to do with his power. Moran, who did only hit four homers in just under 250 at bat's in 2013, has a sweet left-handed swing which allows him to get a hold of balls on both the inside and outside corners of the plate. Moran still has a lot of power to tap into, but with the Marlins current lack of power hitting prospects, he probably has the fifth most current power.
Rosa is the least known player on this list, but his 23 homers were the third most in the Sally League and the second most of the entire Marlins organization. Rosa has the most brute power on this list and he used the hitter-friendly NewBridge Bank Park to his advantage. Next year will be the true tell-all of how much of that was playing in Greensboro and how much of his power is for real. Either way, Rosa uses his 6'3'' left-handed swing to generate enough power to stay on this list. Rosa is more of a future Quad-A guy than a Major League regular but I expect him to put up huge power numbers wherever he plays in the future. Rosa comes in at an impressive fourth on this list, despite being far less proven than some of the other names.
Canha, 24, is the best first baseman in the Marlins farm system, but that's not saying all that much. Canha played his first season at Double-A in 2013, and while he only went deep 13 times, his ISO of .176 led the Jacksonville Suns. Also, one should take into account that the Suns' ballpark, Bragan Field, is one of the harder places to hit for power in the minors. Canha, a 6'2'' 200 lb right-handed hitter, has proven that he can hit it out to all areas of the ballpark. His home run numbers have fluctuated greatly, going from 25 in 2011 to a mere six in 2012, and that's one reason why he's not higher on this list. Nonetheless, Canha definitely has some very real pop and he's very deserving of being third on this list.
Dietrich had a rough 2013 season no matter how you look at it, but he still managed to hit 20 homers between the majors and Double-A. Dietrich has 54 home runs over the last three years, which is pretty sexy for a second baseman. Another left-handed hitter, Dietrich hit the third-most home runs out of second basemen in the Southern League despite playing only 63 games. Due to his results in the majors and in the high levels of the minors that others on this list lack, Derek Dietrich comes in second for having the second-best current power tool in the Marlins farm system.
Jensen is far and away the player with the most in-game proven power on this list. No other player in the Marlins farm system comes even close to Jensen's 52 homers over the last two seasons. Jensen, 25, is a right-handed hitting corner outfielder who strikes out way too much and struggles to hit for average. Nonetheless, Jensen's very real power could earn him a bench or platoon role on the 2013 Marlins. Kyle Jensen has the highest current power tool in the Marlins minors, but that's not to say it's any higher than a 55 on the 20-80 scouting scale.