Choose any Decepticon from any series. My favorite 3 would Megatron, Starscream, and Soundwave. I would say BW Megatron, but he's technically a Predacon, who are just descendants of the Decepticons. :P
 

I bet everyone will probably say the same one  

STARSCREAM!

your picture has my three favorites. sound wave megatron and starscream

" I bet everyone will probably say the same one   STARSCREAM! "

"I bet everyone will probably say the same one   STARSCREAM! "

It's Starscream!!!

I have severalll..... But most likely Starscream... :):)

Megatron hands down, his origin trade was the best Transformers book I read in a very long time, probably twenty years :)

Waspinator :p

Starscream!

Soundwave is awesome

My favorite was always Astrotrain.  He combined my childhood interests in toy trains, space travel, and giant murderous robots all at the same time. 
 
Anytime there was an episode about space in the second season, you knew A-T was going to be in it.

Well I grew up watching armada so I like Megatron.

Soundwave!

Megatron.

Megatron, Starscream, Soundwave and Shockwave are mine.

Beast Megatron is the best written character in any TF story. 
 
But Decepticon... Starscream.  Of course Beast War's guest appearance of SS was epic.

Starscream, Shockwave, Astrotrain, soundwave, frenzy, Rumble, Scrapper... The list is grand

I have many favorites in order:

1. Megatron

2. Shockwave

3. Soundwave

4. Devastator

5. Starscream

6. Galvatron

7. Thundercracker

8. Skywarp

9. Rumble

10. Cyclonus

There's nothing I don't love about ol' Starscream.

Starscream for life is my number one but other then him Brawl sound wave rumble just to many to name really .

Bruticus is my favorite Decepticon, an' not just favorite Decepticon but also my all-time favorite Transformer. Brawl is a close second.

MY TOP 10 FAVORITE DECEPTICONS (decided ta show ya my top 10 for fun):

1. Bruticus (as I already mentioned).

2. Brawl.

3. Devastator.

4. Lugnut.

5. Breakdown (but only from TF Prime).

6. Megatron/Galvatron.

7. Trypticon.

8. Onslaught.

9. Long Haul.

10. Blackout/Grindor.