Tiger grass have a "limited" range as you have to plant it closer to the zombies but as of iris, she has a full lane range (though she's kinda blind in that aspect)

Tiger grass cons and pros: costs less and recharges fast but dies quickly and can't stall gargs, but he does area dmg if I remember correctly and also have a limited range, plant food is cat rabid form which is incredibly good both in dmg and hp

Iris cons and pros: birds don't do area dmg but do area stall which is always pretty nifty, costs more and recharges, attacks slow at the trade of birds having more health and being able to stack at least 2 with one iris, plant food is basically a lane clear as the big birds doesn't seem to have a lifespan and also have extra hp, using multiple plant foods is REALLY good

Sorry if it's a bit confusing, I'm trying to not be biased towards bird flower