Ooh, this was hard. I love everybody on the list except of Tara Strong.

I'm not much of a Tara Strong fan either, though I must admit I do think she voices Twilight pretty well. She seems to give her a bit more personality and emotion than some of the other characters she's voiced before.

The ones that impress me the most in the series are Ashleigh, Andrea and Cathy. I think they voice their characters spot-on and really can't think of any way they could do it better! The sounds of their voices suit their characters, and they always seem to manage to get the right emotions for them too. That said, I think all six people listed here do very well.

It was difficult to pick between those three, but Ashleigh Ball got my vote just because I think I like her singing voice the most out of all of them. So I'll give her a bonus point for that!

I love her Applejack voice

SOOOOOO HAAAAAARRRD. They're all ridiculously talented, and voice their MLP characters as beautifully as any animated character has ever been voiced.

I have to go with Ashleigh--she does my two favorites, who sound very different and have awesome voices; she sings wonderfully, and she's also Plum Pudding, one of my favorite Strawberry Shortcake characters...who happens to sound just like a sliiightly higher-pitched Rainbow Dash!

But Tara is amazing. Not only is she a sweet, funny lady (she even added me on Facebook!), but MAN, I cannot believe her ability to change her voice. O_O So, many, different, characters...and she's worked on some favorite shows of mine, including Fairly Oddparents.

Andrea (also in Strawberry Shortcake, as Lemon Meringue, who sounds rather a lot like Pinkie) and Tabitha are also brilliant voice actors whose MLP work deserves awards. Nicole is perfectly suited to the regal, yet lighthearted, Celestia, and Cathy's Spike voice is equally PERFECT for a young dragon...so distinct, so cute, so little-boyish!

Meh, I don't care for Tara much at all. I LOVE Tabitha, simply because the variety of voices she can do is amazing. She voices Rarity, Luna, Zecora, Photo Finish, and a ton of others on the show.

To me, Tara is an amazing voicer...person. She voices some of my other favorite characters. But, Pinkie Pie and Fluttershy's voice? From Pinkie Pie's hyperactivity and Flutter's bashfulness, who can do that? It's beautiful! I honestly think this deserves an everyone's voice button, but I'm too lazy to add one. -_-

I love Tara Strong! She has an awesome voice!

I'm not really into many cartoons, so I'm not very familiar with the actresses outside of MLP:FiM.
All of the voices are so perfect! (Another reasons to adore MLP.) Applejack is my favorite pony, and I also love Rainbow Dash. Their voices are excellent, and I always love their singing. So that means my definite choice is Asheigh Ball!
I really appreciate and am amazed at the diverse voices of these actresses, e.g. Tabitha St. German and Andrea Libman.
It's also really fun to look up MLP voice actors and see what else they were in. I found a lot of things I love or recognize.

@SouthParkSmart: And Granny Smith!!! :D :D :D (which, of course, you included in "and a ton of others on the show"). But yeah... I love Granny Smith. :)

^ Oh yeah, I thought of her after I posted. :-)

She ALSO voices Princess Luna!

She's amazing! Fluttershy's and Pinkie's voices are well-done and great! I also love Tabitha St. German; she's great with all of her characters! :3

Man so hard to choose I like all the voice actors

Tabitha also voices Luna, Granny Smith AAAAND Derpy.

Pretty darn awesome.

Wait really

and Andrea Libman

She's like perfect. I loveeee both pinkies and fluttershys voice so much. I dont really like any of the others voices..i think they should have picked other people for all of them but both of these are perfect..i like RD voice but AJ's is the ugliest thing i've ever heard. I liked her until i heard her talk.

They all play their parts so well!