Get ready for a wall of text as usual. I apologize in advance.

OCs can be quite good with the proper effort and the right frame of mind; in fact, some of the most interesting ponies I know are OCs. As long as they are not overpowered and fit in with the world, i.e. not canon destroying, as well as having a thought out and interesting story (and talent). Fortunately, we seem to have avoided the fate of the Sonic fandom with huge amounts of edgy recolours and mix-and match characters made in an OC creator*, as that has thankfully (mostly) dropped off here due to the staunch stigma in the Brony fandom against "black and red alicorn OCs who are related to and/or in love with the mane 6".
Also, I dislike "ponysonas", not by themselves (they can be good for some things), but when used in a "real Equestria" setting; really, it's no different from a self insert, and most people end up over-playing their talents or abilities.
Back on track though, most OCs of our day are pretty good, and I enjoy seeing well-made ones.

*Clarification: I don't have a problem with the pony maker or those that use it, as it is pretty good for some things (if used properly). However, I don't feel it is really suitable for a "serious/realistic" character, and it is annoying to see too many at once. Also, it allows for some hideous combinations.

If anyone wants more clarification or to counter what I said with their opinion in regards to this, feel free. I feel up to a bit of a debate tonight.
-DarknutLord

https://www.youtube.com/watch?v=Cq8_tDJpePk

Caller: Hello, I am here to talk to you about (candidate)
You: https://www.youtube.com/watch?v=kVZhsiLCkHE
Caller: (repeats name)
You: http://youtu.be/kJta7nw6fAM
Caller: He's the guy running for (position) in your district. Are you voting for him?
You: http://youtu.be/UmRGkOPo-9E
Caller: Really? I think you should. The-
You: http://youtu.be/UgYIYCJxrbY
Caller: All I was going to say is that (statistic).
You: https://www.youtube.com/watch?v=-mrmBe-fFr4
Caller: There's no need to talk like that.
You: http://youtu.be/rnPfpSja5tk?t=2s
Caller: *Frustrated* All I want to know is who are you voting for?
You: http://youtu.be/3HbRg2CdokA
Caller: *Wat* Are you changing your voice?
You: https://www.youtube.com/watch?v=fxhExEp1FLY

Neon Lights, voiced in the fandom by ShadyVox. http://www.youtube.com/watch?v=2dEuNen6CDs