What are some good units for the blessed Gardens?

grima goes great with Ephraim imo. the +4 def is just amazing on him but the same thing can be said for gunthra and the +4 res.

bike is good with Earth Blessing

Water team- Lyn (merged +2), Fjorm (merged +1), Raven and Azura (merged +2)
Fire team- Grima Robin, Ayra, Bride Lyn (merged +1), and Legend Ephraim (merged +1)
Earth team- Legend Ike, Micaiah, Sothe, and Perform Azura (merged +3)
Wind team- I don't have gunnthra yet so I just gave one of my most used teams wind blessings. Joshua (summon support), Dorcas, Perform Olivia (merged +3) and Reinhardt (merged +6).

These units can work with what you got for each kind of blessing specifically.

To have synergy with Legendary Heroes since I don't know which units do you have:

Fjorm: A fast unit, so you don't have to use the Spd 3 seal. Also works to make slow units quite fast (like Nowi, but she's better with QR). Ayra, Mia and Caeda to activate Flashing Blade.

Gunnthrá: Any unit that debuffs a lot of stats. Ploy users are good candidates, since the +4 Res helps them (like Arvis and Lute) and some Daggers (using a refined Smoke Dagger, Dual Smoke or Sothe). Any mage tank works too (like Felicia), mixed tanks and units with DC to counter magic or Iceberg/Glacies.

L!Ike: Any unit with a Brave weapon, specially Reinhardt, Elincia, Cherche, Effie… and units using Heavy Blade. Also, units with nuke/one-shot potential (like Julia or Sanaki).

L'Ephraim: Armor units are good with it, in case you're using one with Armored Boots or Armor March. Also, physical/mixed tanks, units with CC or to increase Bonfire/Ignis power.