Like:

Belethor
Marcurio
Aela
Dark Brotherhood initiate
Delvin Mallory
Vex
Parthurnaxx

Annoy:
Naseem
all the old hag voices
every kid voice
Elf that runs Black Briar brewery
Ulfric Stormcloak
Heimskr
Night mother

Karliah and Vex

There are only so many so I am just going to pick two:

Best voice: Molag Bal, so very sixy and dominating.

Worst voice: Karliah, shut it you damned big headed elf!

Sheogorath > All

Don't know about my least favorite voices... probably the children, of both genders.

Love: Ulfric (I can go talk to him just to hear his voice!), Karliah, Sybile Stentor (that actor doesn't always sounds that good, but in Sybile's case she sounds so - pleasant.). The female Altmer VA sounds snotty in most cases, but Niranye sounds really, really nice.

Hate: Nazeem and the gazillion other NPCs voiced by that actor. He does a good job, I can't deny that, but he sounds so - sleazy. Which is ok when he does unpleasant or evil characters, but totally wrong when he does for instance that young guy in Ivarstead who's in love with Fastred. And Elisif - that actor also does lots of voices, and mostly she sounds ok, but Elisif just sounds so whiny. "Bohoo, now's Ulfric's gonna be High King and I broke my NAIL!"

Any Dunmer voice is terrible. Why oh why did they ever decide to make them this way. Morrowind had the best voice for them.

Likes:

Esbern
Aela
Brynjolf (come to think of it, most of the TG voices are good, except for: see below)
Marcurio
Meridia

Dislikes:

Ulfric
Karliah
Arngeir
Any NPC who sounds like the tree-hugger from Blessings of Nature

Like:

Tolfdir
Marcurio
Aela (and anyone else Claudia Christian voices)
Marise Aravel (and anyone else Lani Minella voices)
Lydia (and anyone else her VA voices, like Dinya Balu, for one)
Delvin Mallory
Vex
Arngeir (Christopher Plummer could read the phone book and I'm there!)
Esbern (ditto Max von Sydow)
Khajiits (both male and female)
EDIT: Ooh, forgot Brynjolf!

Annoy:

Naseem (probably more his manner than his voice, really)
Ulfric Stormcloak (a lot of people were practically wetting themselves when it turned out that Vladimir Kulich was voicing him but I just don't find him that compelling)
Farengar Secret-Fire (darn, he voices Vorstag, my current follower, too!)
Edda/Silda the Unseen (I think they're voiced by the same actor?)

Likes:

Esbern - agree
Aela - agree
Brynjolf (come to think of it, most of the TG voices are good, except for: see below) - agree
Marcurio - agree
Meridia - agree
Most guard voices

Dislikes:
The female elf that runs the clothing store in Solitute
Septimus sigmus
Cicero
Calcemo

Cicero. Period. Most annoying voice in a game ever. The only thing that would be worse is if Fred started playing Skyrim and started talking to Cicero.

Best voices: Karliah, Brynjolf, Serana.

Voices I like/love:
Ulfric
Arngeir
Paarthurnax
Esbern (but then I'd watch a video of Max von Sydow reading the phone book out loud, so...)
Bothela (and whoever else shares it)
Marcurio (and whoever else shares it)
Balgruuf (and, apparently, 99.9% of the male Nords in the game )
Idgrod (may be the same as Bothela - anyway, thumbs up to wacky badass old chicks everywhere)
Every single Khajiit in existence

Voices I dislike/hate:
Aela, Adrienne Avenicci, Iona (I think these may all be the same person. Currently the voice I loathe the mostest)
Belethor (and the approximately 3 million other characters with the same voice)
and... that's all I can think of. Most of my voice hate is reserved for a couple apparently ubiquitous and, to my ears, extremely grating examples.

Yup, all voiced by Claudia Christian.

Belethor really really annoys me. He voice is just too loud and obnoxious. I know that voice actor voices multiple characters, but for some reason Belethor in particular annoys me.

He annoys me, too, but more because he's sleazy than because of the quality of his voice!

I think the guy that does Belethor also does TG Mercer Frey

the guy that does Marcurio also does all the Courior voices

let's play the voice list game....

Least favorite: Farengar, Nazeem, any Thalmor, Aela, Belethor, Jarl Elisif, Mjoll... yeah, there's too many to count.

Favorite: Jarl Balgruuf and all those typical Nord characters.

Best? Probably Arngeir voiced by Plummer.

Worst? Probably the Thalmor, speaking with that almost unbearable smugness.

I love Farengar Secret-Fire's voice.

I like Boethiah's voice, and the actress who does Vivienne Onis and Sybille Stentor

I dislike Farengar's voice

I've grown to almost despise that Swedish- (or whatever) sounding woman that does Mjoll and seemingly thousands of other characters. My heart dies a little whenever I hear her. Her performances are uniformly flat, and the accent (after 400 hours of play) just gets on my damn nerves for some reason.

Cicero has by far the most annoying voice in the game.
I like but his voice is just so loud and shrill.

Like: Baalgruuf, Ulfric, Khajiiti, Esbern, Paarthnuax, the Claudia Christian NPCs (but there are too many of them! Wish she had been held in reserve for Rikke and Potema.)
Hate: Farengar, Belethor, Brynjolf
No so hot about: Dunmer voices

I love Cicero's voice. He always puts a smile on my face whether he's talking, singing, or in combat, I love it. ?

I love Nazir and Babette voices.

Most hate is : DARK BROTHERHOOD'S DOOR!! God, I hate those doors...