Blovers are more useful unless you are playing Survival: Pool (Hard), Survival: Fog (Hard) or Survival: Endless. On top of that, Blovers can be used when there is no water.
Cattail by a MILE!! Note the picture on my wordbubble!!
Although I prefer the Blover plant, I think the Cattail is far more useful, as it can kill nearly any Zombie, and helps win nearly any Pool minigame. Blover only helps a lot in fog. However, I still love Blover and it will be my 2nd favorite Plant, but Cattail is undeniably more useful. Stay Naughty!
Cattail is useful in pool and fog levels because they can shoot anywhere and two of them are enough to take down all Balloon Zombies. I use Blover in day, night, and roof.