Hey guys! So I found this really awesome tier list that iDream from Cloud 9 put up for Heroes of the Storm. Here's a link: C9 iDream's Tier List for HotS(Heroes of the Storm)
Also on the website is Zuna's Tierlist broken down into tiers based on champion strengths rather than classifications (tanks/assassins/etc) as well as the current Free Hero Rotation and a ton of other Useful tips and links. Lastly, there's a dropdown next to each of the heroes that shows you the build you should use for the best results.
However, if you just want the info in iDream's list, here's a simplified version:
Best to Worst (Left to Right)
Tank: Arthas/Stitches/Muradin/Chen/Tyrael/Anub'arak/E.T.C/Diablo
Ranged Assassion/Carry: Tychus/Valla/Falstad/Tassadar/Sergeant Hammer/Jaina/Raynor/Nova
Specialist: Nazeebo/Zagara/Abathur/Gazlowe/Azmodan/Murky
Melee Warrior: Zeratul/Kerrigan/Illidan/Sonya
Support: Uther/Brightwing/Rehgar/Li Li/Malfurion/Tyrande