Blanket Rejuvs are only ever strong, in raids, near end of xpacs when you have the haste to reduce the GCD down far enough.
Balance (only take guardian for fights with no range problems like Cenarius or Ursoc)
Spring Blossoms (inner peace can bring you more HPS in some fights but in reality it is just sniping heals that would have come from other heals anyhow)
*I see that cultivation has been buffed significantly and the hard cap on hots gone for mastery so now, combined with enough haste, blanket Rejuvs will be strong. I've never liked the requirement of them having to be below 60%. I have a feeling that the Nighthold raids require a lot more healing than EN with players going low enough health many times during a fight. This will make Cultivation much stronger due not only getting the proc, but also getting that extra hot benefiting more from your mastery.
Rdruids are all about preparation. The better you know a fight, the better you will do. If you know people are about to take damage you can have Rejuvs on them beforehand. Swiftmend for the SoTF proc before they take damage, allowing you to react with WG as quickly as possible. Follow up WG with Flourish only if they close to 50% of their health in damage.
Flourish can be weird sometimes and not take. You want to make sure to wait a fraction of a second before popping it after a WG. I try to refresh a Rejuv or Lifebloom on a tank in between WG and Flourish for max efficiency instead of waiting.
RDruids are not reactionary healers. You should not be spamming Regrowth or HT at all. Most of the time Regrowth will only be cast on OoC procs. Cast your Lifebloom, Rejuv and occasional Ironbark on tanks and leave the heavy tank healing to classes more suited to single target healing. RDruids always have been raid heals. Obviously if your tanks are about to die keep them alive but your Regrowth spam will barely tickle their healthbar and devastate your mana. If you find yourself in a situation where one or two targets are taking damage a Regrowth followed up by a HT isnt a terrible idea. It's just not very mana efficient, fast, nor are your single target heals quick and strong.
Strive for 100% uptime on Lifebloom and Efflorescence. Even if you cast it under just the two tanks, Efflorescence is extremely efficient. Lifebloom does not always need to be used on tanks, you can use it on players who start taking a lot of ticking damage too(for example Rot on Nyth). WG+SoTF is your bread and butter and should account for close to a third of your heals in a fight. Blanket Rejuv as necessary so long as you have the mana reserve. Don't use your SoTF proc on anything but WG.
Usually you get 2 uses of your Tranquility and Innervate in the fight. The first time you use either is not very important as long as it's within the first 90 seconds. The second is crucial and can make or break a pull for you and your raid. Most fights dont need a Tranq early on and it's simply used the first chance the entire raid takes damage in order to save mana for you and your fellow healers.
Turn off your healing meters during fights. You should be looking at your mana vs other healers mana not your HPS vs other healers HPS in the middle of a fight.
Stat Priority should be:
*Mastery got a slight buff, no longer having a hard cap on the number of hots that apply the bonus. Mastery will now be stronger in raids, especially on fights which have a small number of high damage targets. Supposedly this was unintended as some hots were being considered the same and would not apply another bonus when active at the same time.
*If you are looking at HPM with logs/parses or whatever theorycrafting you do you will come up with with a much different stat weight. Here is why.
*Haste stat weights usually do not take the GCD into account. Versatility stat weights usually do not take the damage reduction into account. Crit is gonna matter more for fights where your Tranq is key to surviving. Every fight is gonna be different and require different kind of healing. Fights can be long, short, bursty, or spread damage; this means each stat will have a strength over the others in each scenario.
Darkmoon: Promises is still going extremely strong, espeicially if you go cultivation over SotF.
The top four leading to Dreamwalker will give you the most increase in output. The bottom route heading to Power of the Archdruid will give you more mana utility for those longer fights, but less healing output the higher the dps of the group you're in. Going for Tranquil Mind last is the best option. The only fight I can think of where it would help tremendously is Renferal.
It matters not which of those routes you take first as the power required to fill both is small. It's really your preference.
Dungeons are where the blanket Rejuv style will be super strong.
Entire dungeon maintain 3+ Rejuvs minimum, if not more. You have plenty of mana and occasionally out of combat moments to get your mana back by drinking. It can be intense to keep up Rejuvs the entire dungeon but will allow you to hit 1 sec cast times on your HT allowing you to do some amazing spot and tank healing.
Edit: spelling, grammar and added stuff, things, and clarification
Edit 2: updated a bit for 7.1.5 patch but not finished