For raids & dungeons all stats are roughly equal, depending on what gear you are wearing it can change very slightly. I advise using online tools such as WoWAnalyzer or QuestionablyEpic, to get very specific numbers.
Mastery (Mastery: Harmony) - Each HoT we have on a target increases our healing on them, by a moderate amount. You will always get value from this, especially when dealing with high single damage. It is also strong when ramping and using cooldowns, during high damage.
Critical Strike - Increases the chance for each heal and damage ability to crit, this includes all HoTs.
Haste - Like other classes, haste reduces your cast time and lowers your GCD. In addition, it also benefits our DoTs and HoTs by giving us a partial tick at the end of their duration.
Versatility - A fairly bland stat that increases your damage / healing, while also reducing damage taken.
Your stats may vary heavily as to what is best and worst; the best way to know, what is strongest for you, is by using one of the tools available which I will list below.
WoWAnalyzer - https://wowanalyzer.com/ an amazing site for reviewing your performances and figuring out what stats are best for you.
HealerStatWeights Addon - https://wow.curseforge.com/projects/healerstatweights
For Alliance the best race would be Nightelf due to its ability to shadowmeld within dungeons and it has an okay passive for raid content.
As for Horde the difference between a few races is very minimal so it mainly comes down to preference.
Troll - Berserking gives you an additional cooldown to ramp with.
Zandalari Troll - Embrace of Pa’ku is the highest throughput passive racial but offers very little elsewhere.
Highmountain Tauren - With this race you gain 1% vers and a strong mobility cooldown which may come in handy on occasion, although as a druid this may go to waste.
Weapon - Machinist’s Brilliance
Ring - This is dependent on which stat will net you the biggest increase.
Intellect Gem - Leviathan’s Eye of Intellect
Mastery Gem - This is dependent on which stat will net you the biggest increase.
Food: Baked Port Tato
Healing Potion: Abyssal Healing Potion