Stalkers are the ones that say stuff like "I'm here in the shadows" right? If so, them, because they sound so cool. I haven't played much Protoss to have a favourite for any other reason.

6 pylon 4 life.

Mothershiiiiips

Only good Protoss unit, is a dead Protoss unit.

Stalker because blink micro is super fun.

I like Stalker's gag lines.

I'm a fan of High Templar.  I don't always use them, but when I do, I'm happy.

dark Templar's are devastating against a unaware player
and they are just plain badass

I always love some sentry defensive action!

" Mothershiiiiips "

High Templars crush everything.

Them zealots are sexy and badass at the same time.

It's hard to choose, I like a lot of the units so either the Mothership or a Void Ray.

A dead Protoss unit, (Or Dark Templar's, they are bad ass).

Fenix

A handful of High Templars + Psi Storm = 100 dead marines... a SECOND! (100DMPS)

It was a Dragoon, but now its a Colossus. Can't wait to see Dragoon units in Legacy of the Void.

I love the sentry. Best unit in the game for T1.

My life for Aiur!

Archon. Although it takes 2 High or Dark Templar to merge to create one, their health is almost completely shield based, and since that regenerates, they are really tough nuts to crack.

Immortal!

" It was a Dragoon, but now its a Colossus. Can't wait to see Dragoon units in Legacy of the Void. "

Zealots. Few guys can wreak so much havoc on enemy economy like those guys, with the charge ability, if you manage to drop them in the middle of your opponent's gatherers.

" Only good Protoss unit, is a dead Protoss unit. "

Zealots simply because they look badass.  And they charge headfirst into enemy fire without fear.  
 
Chargelots are without a doubt my favorite unit in the game, it's so great to see them rush to surround a group of baddies.

DT's are awesome!

Probe.  Everyone that didn't answer probe is wrong.

Carrier has arrived.