A best of is really, really hard, but some just get to you more than others.
Some of the first favorite books of the very little herring:
The very hungry caterpillar by Eric Carle
Something by Richard Scarry (don't remember the title)
I Am Me by Mira Lobe, the story of a little craeture thatis like no other animal and takes a while to learn that that's okay
later on (Mostly Germans will know these):
Also Kalle Blomquist (aka Bill Bergson) and Ronia the Robber's Daughter by Astrid Lindgren and Jim Knopf (aka Jim Button and Luke the Engine Driver) by Michael Ende.
All of these will one day be read to my future kids, whether they like it or not. Mua hua hau!
Then as I started reading on my own rather than being read to it was mostly adventure stories and/or stories that took place in foreign cultures or different eras with kids being thrown into adult situations. And then there was this collection of real historic adventures (like parts from the log book of Columbus, the story a nobleman who nearly got executed during the French revolution, the report of a doctor who treated the infamous prisoner with the iron mask, etc.)..I loved it.
Edit: Also a youth magazine' s series on science and history (still trying to get my hands on some copies again). And then there was loads of Karl May, Around The World In 80 Days (I loved Phileas Fogg) and The Three Musqueteers by Alexandre Dumas. We three kids used to play musqueteers, I was usually Athos (or Mylady de Winter, she was badass), my sister was Porthos and my brother d' Artagnon. We had no Aramis.
What an oldfashioned childhood that was considering there was Nintendo around already!