The following is my personal opinion.

Before season 3 there is the Intermediate Season which includes the Japanese manga that has been released in English my Viz media. The Japanese OVA scramble city, with an unofficial continuation as a fan made video and an official continuation as a Japanese Manga posted online, I have added a link to a fan translation. Finally, of course Transformers the movie.
M = Must watch: Major plot event and introduction of character/s.
N = New Characters: Not a major plot event but introduces new character/s.
F = Fun Episode: A fun episode to watch.
S = Skip: Boring and or bad episode.
| Title |
Importance |
Comments |
| Prologue (Manga) |
S |
Not bad but is a recap |
| Chapter 1 (Manga) |
M |
Decepticons Attack japan / Introduction of Kenji and Autobot communication Helmet |
| Chapter 2 (Manga) |
F |
Decepticons corner bumblebee in japan |
| Chapter 3 (Manga) |
F |
First Mention scramble city and Trypticon |
| Chapter 4 (Manga) |
N |
Introduction of Ultra Magnus / Autobot Road |
| Chapter 5 (Manga) |
S |
Just a combiner teams battle. |
| Chapter 6 (Manga) |
N |
Introduction of Trypticon / Metroplex (Only as a hologram) |
| Chapter 7 (Manga) |
F |
|
| Chapter 8 (Manga) |
S |
Has animal cruelty. |
| Scramble City: Mobilization |
N |
Introduction of Metroplex. Ends on cliffhanger. |
| Scramble City 2 |
F |
Fun made continuation |
| Scramble City 2 Manga |
F |
Official continuation made years later |
| Transformers the movie |
M |
Just watch it, if you have not seen it. It's fun. Introduction of too many new characters to list and the introduction of the Matrix of leadership and evil Unicron. |
