Since this is becoming a common question and people are having issues choosing which rainbow to get this week, now's a good time to break down which rainbows are good in the future.

(I have no idea why I typed all this out for you lazy bastards. Who actually chooses rainbows based off of stats instead of looks? etc.)

As a general rule, base/evolved passives only still apply if they aren't overwritten. For example, if a girl gets +10% def when evolved, but +20% when bloomed, the 20% def is what takes priority. If something isn't listed, assume their base/evolved passive still applies (like ignore movement panels passive).

For those who want the tl;dr: Dendrobium, Black Baccara, Ionocidium, Lycoris, Lagurus, Mistletoe, Saffron, and Apricot are all great choices.

* denotes new passives. Otherwise, overwritten passives will be noted in parentheses, using the notation (previously X).

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Black Baccara:
*1.2x skill chance based on affection (new)*
+65% atk on self + 1 ally (previously 35%)
*+10% more atk on party (new)*
+22% def on party (previously 15%)
+4% guard rate (previously 2.2%)

Dendrobium:
+22% atk to whole party (previously 4 units only)
*+10% more atk to self (new)*
*100% chance to attack again on first turn, 2x self skill activation also procs on the second attack (new)*

Cattleya:
*1.2x skill damage based on affection (new)*
+40% atk (3 party members including self) (previously 27%)
*+15% skill damage (new)*

Alpinia:
*1.2x~1.32x skill chance (based on skill level, not affection as usual) (new)*
+20% atk (previously 15%)
*100% counter w/ 3.75x defense power (new)*

Cactus:
+20% party atk (previously 15%)
*+15% crit (new)*
*60% chance to attack again (new)*

Mei Plumblossom:
*1.2x skill chance (all turns) (new)*
+18% party atk (previously 15%)
*+15% crit (new)*

Sakura:
*1.2x skill chance (all turns) (new)*
+18% party atk (previously 15%)
*12% more damage on raid bosses (new)*

Fritillaria:
*1.2x skill chance based on affection (new)*
+20% party attack (previously 15%)
*+15% crit (new)*
+16% self attack for every party skill used, up to 96% (previously +2%, up to 30%)

Flowering Peach:
+20% party defense (previously 15%)
+3.7% dmg reduction while guarding (previously 2.2%)
*+10% party crit (new)*
*Against bosses, +15% party atk and +8% party damage (new)*

Anemone:
*+25% party crit (new)*
100% chance to counter for 4x defense (previously 3.5x)
*+25% party atk (new)*
+22% party def (previously 15%)
+4% dmg reduction while guarding (previously 2.2%)

Dogwood:
1.2x skill chance (new)
100% solar blast gauge at start (new)
+25% attack per solar blast use, up to +75% (previously +14%, up to 42%)
+70% solar drive effectiveness (previously +40%)

Daisy:
*1.65x skill chance (first turn) (new)*
+35% atk (herself + 2 members) (previously 30%)
*-2.1% damage taken (new)*
*+10% crit rate (new)*

Kerria:
+40% atk (previously 35%)
+6.8% damage reduction (previously 3.7%)
*80%/80%/50% evasion each turn (new)*
*Increase self damage based on half of current HP / max HP (e.g. at full health, do 50% more damage) (new)*

Cherry:
*+15% party atk (new)*
*+10% more atk (3 members) on raid bosses (new)*
(if this doesn't seem like much, it's because her -15% atk on enemies was already too good)

Dianthus:
1.2x~1.32x skill chance (based on skill level, not affection as usual)
*Against bosses, +20% party atk (stacks with previous +20% attack based on affection) (new)*

Ionocidium:
*1.2x skill chance based on affection (new)*
+18% atk (previously 15%)
*80%/80%/50% evasion each turn (new)*
*40% chance to attack again (new)*

Nerine:
*1.32x skill chance (based on skill level, not affection as usual) (new)*
+25% atk (previously 15%)
*+22% def (new)*
*+4% dmg reduction while guarding (new)*

Victoria:
(bloom announced, no info yet)

Lycoris:
*1.2x skill chance based on affection (new)*
*+15% more atk for every enemy in battle (new)*

Oncidium Bride:
(no bloom yet)

Lagurus:
*100% chance to attack twice on first turn (new)*
*+120% damage based on party's movement speed (new)*

Helenium:
(bloom announced, no info yet)

Maple:
(no bloom yet)

Pumpkin:
*1.2x skill chance based on affection (new)*
+18% atk (previously 15%)
*80%/80%/50% evasion each turn (new)*
*Three party members (including self) can deal 1.5x damage to enemies weak to magic (?) in addition to their type (new)*

Viola:
*1.65x skill chance (first turn) (new)*
*+3.7% def reduction (new)*
*Three party members (including self) can deal 1.5x damage to enemies weak to pierce (new)*

Mistletoe:
*-15% atk/skill rate for enemies (new)*
+22% atk (previously 15%)
100% counter w/ 3.75x defense (previously 3.5x)

Christmas Rose:
(no bloom yet)

Ardisia:
(no bloom yet)

Herbaceous Peony:
(no bloom yet)

Acacia:
*+10% crit to party (up to 80%) (new)*
*+40% more crit to self (up to 80%) (new)*
(same thing as Cherry, she already has good base/evolved passives)

Wax Vine:
(no bloom yet)

Burning Bush:
*-20% enemy skill activation (new)*
+20% atk (three members) (previously 15%)
*Three members can deal 1.5x damage to enemies weak to magic (?) in addition to their type (new)*

Mimosa:
(no bloom yet)

Apricot:
*1.2x skill chance based on affection (new)*
+20% atk (previously 15%)
100% counter w/ 3.75x defense (previously 3.5x)
*Once per battle, negate one attack for each party member (new)*

Saffron:
*+30% def (new)*
*+5.3 dmg reduction (new)*
*100% counter w/ 4.25x defense (new)*

Snowdrop:
(no bloom yet)

Iberis:
+20% atk (previously 15%)
*+12% enemy miss rate (new)*
*Three members can deal 1.5x damage to enemies weak to hit in addition to their type (new)*

Hollyhock, Habranthus, Victoria Bride, etc.:
(no bloom yet)

nice, thanks for the info

Originally Posted by Eab1990

Lycoris:
1.2x skill chance
+22% atk
15% enemies? (gonna need clarification on this)

It increases the party's attack power by 15% multiplied by the number of enemies at the start of the battle. If there's three enemies, she increases everyone's attack by 45% + 22% from the other passive.

Apricot's ability is once per battle, not once per turn, though it's still incredible. Dendrobium's double skill chances do apply for her double attack (other double attacks also benefit from the first-turn buffs of Cymbidium, Daisy, Anthurium etc. if they trigger on the first turn).

It's worth noting that Lycoris' blooming is so overwhelmingly powerful (who needs stats when you have the best offensive ability and second-best defensive ability in the game?) that she should be an instant pick for min-maxers, but her blooming is late enough that it won't be too relevant to Nutaku players. If you're in for the long haul, you'll also want to pick up a dodge rainbow (which Lycoris is) for the amazing synergy between dodging and the attachable taunt ability, which will make you all but immune to non-skill attacks.

But yeah, I agree that rainbows should always be chosen based on looks. There aren't many maps that require min-maxing, even on DMM, and these that do exist can mostly be cheesed with the right golds.

Thanks, updated main post.

Hmmm a lot of mine do not have bloom forms.... not that I really care they are all too cute to need them anyway.

Herbaceous Peony: (no bloom yet)
Snow Drop: (no bloom yet)
Christmas Rose: (no bloom yet)
Oncidium Bride: (no bloom yet)
Flowering Peach: (no bloom yet)

Great post Eab, thanks heaps.

Question for you, why doesn't Alpinia make your top selections list? Her low Attack is boosted by the +20%, and then she gets the counter with 3.75 x Def. Looks very powerful to me?

So, I found myself with an unexpected 6 star ticket. (SenPro closure). Current rainbows: Maple, Alpinia, Oncidium Bride, Black Baccara, Dianthus, Acacia, Pumpkin, Cherry, Flowering Peach, Dendrobium, Anemone, Mei, Burning Bush, Helenium, Lycoris, Mimosa, Ardisia. Recommendations? I was leaning towards Iono, Kerria, or Apricot.
Edited: I got Saffron also in the last sale.

Only gold, just gold is matter for preparation. Petal/bloom bird should be dropped as quest reward. Elixir is farmable. (Drop rate is about lv.100 dragon drop) But gold is scarce as it is used for so many things.

If you seeking for single broken damage on single target Kerria can give you.
If you want super defensive Apricot is your choice.
If you need dodging unit for future broken map Iono can help you.