I have to go with the Flinx. They were EXACTLY what Summoners needed preboss - a reliable minion that’s readily available (Flinxes aren’t that hard to farm if you understand how they spawn), and before any real combat. They work well enough for the King Slime and the Eye, and help to secure the Vampire Frog once the player decides to bother with that.
But the real reason they are the best is because they look awesome with the little bun, and the way they just throw themselves at the enemy is hilarious.