Among the 3, Bright is the pure healer. Since he keeps healing in permanence and has just 2 "support" skills (decreasing dmg dealt and increased health). Sunny is more of a support since she has 3 support skills (more hp, enhanced ele res, more def). Crocus is more of a support bomber. When she triggers 4th skill she can deal a good amount of dmg, then she boost dmg and health, and she can decrease enemies health pool. I don't know who is the more effective healer with 1st skill, so I can't make comparison in the only active skill they all share So it's up to you and to what you are actually looking for. I would say Bright as healer and Crocus as substitute bomber or just as an unconventional healer in a high offensive team.
DeusEx87 
Natara 
Storm_Wager 
Jng 
DefyTheRush
I don't know who is the more effective healer with 1st skill, so I can't make comparison in the only active skill they all share
So it's up to you and to what you are actually looking for.
I would say Bright as healer and Crocus as substitute bomber or just as an unconventional healer in a high offensive team.