1. Smash has the best healing out of all the zombies, and it has the strongest selection of gargantuars, this makes smash one of the strongest zombies, so no doubt you will see it often. The sports smash deck is super lackluster, I wouldn't play it.
2. Immorticia is crazy good in beast, which happen to be a top tier zombie deck IMO. They have INSANE early game options such as cat lady, zookeeper, and yeti. Their mid game is kind of lackluster, but octo zombies in the late game is crazy. It also helps that immorticia's special triggers pet twice for ONLY ONE BRAIN (WTF!!!???). For example, at turn 2, it is possible to make a 9/4 cat lady, 6/4 cat lady, and a 2/1 bat (yeah, that's 17 dmg if you didn't draw any early game, and she did).
3. that's why i don't play a lot of low damage plants on the guardian side. I would always take tough beets, but that's about it. I think the mushrooms are rather useless at this point unless you are playing a pineclone deck.
4. guardians counter smash decks by having doomshrooms. DOOM!!!!!!