question: most floriferous

[Maryanne]

Marigolds ? ; -D (oh, April first was yesterday)
I think the plant you choose with those characteristics has to be in exactly the correct conditions to be able to deliver what you demand of it. I have (or had) some of the plants listed above. I obviously have conditions too cold for Phals, and cute Harella (gone) Phrag longifolium hybrid I have grows well enough, but some condition (too cold?) does not exist here to allow it to flower much - winter too long with little sun in New England maybe?
I have a Crystelle Smith, which does OK, but again, it is not in constant bloom. You will have to keep trying various plant selections and manipulating all conditions to keep that plant optimally happy.
Best of luck in your search!
Maryanne