Sky Temple favours three things, in the following order: Globals, Merc Clear, and Boss Control. Globals achieve value during the temple phase by acquiring soak and enabling pushes - the constant threat of a Falstad flying in or a Dehaka burrowing effectively means you're 6v5 on the map if your opponents lack that presence. Merc clear is essential for denying deathpushes, where numerous waves bunch up and sledgehammer through structures, as well as for staying on top of EXP. And finally, Boss Control can shift favour around the level 13-16 mark, where a strong Boss can decide the game.
To that end, lets take a look at a few heroes in each category that achieve good value on Sky Temple!
Globals: Dominated by Abathur, capable of soaking, ganking, and even repairing structures. By far and away the strongest individual hero on Sky Temple, when played correctly. ETC is my tank of choice on Sky, owing to his powerful split-push, ideally paired with a Tyrael or Anub'arak to help lock down bosses.
Merc Clear: Anything goes! Take bruisers with Sonya, rip giants with Hanzo, or take both with Greymane and Maiev - Merc Clear is as straightforward as 'having damage'. The occasional Gul'Dan to save top lane from being death pushed doesn't hurt either!
Boss Control: Holy Ground, Void Prison, Cocoon, Containment Disc, Mighty Gust - look for heroes that already achieve value in the above categories before you look here. The more heroes you have that can fulfill multiple roles, the more flexibility your team has in decision-making. A composition consisting of ETC, Tyrael, Hanzo, Maiev, and Rehgar is poised to deal with virtually any scenario - as is Abathur, Johanna, Zeratul, Greymane, Kharazim.
As an individual player in SL, try to find heroes in your role that can cover multiple duties - the more things you can do yourself, the less dependent you are on your team, making it significantly easier to win.
if you have additional questions, you can find answers at my Discord!