This is what happens when you try Siri, Google, Cortana, and S Voice at once.

Voice-actived personal assistant apps come native on most smart phones, or they can be downloaded from the app store. They promise great interactive help for important (and not so important) tasks, questions, and requests.

But they all can't be the best — so which one should you be using? I checked them out so you wouldn't have to.

I put services up against each other: Apple's Siri, the Google App, Microsoft's Cortana, and Samsung's S Voice. I matched them against the closest thing CNBC has to a personal assistant: intern Shane D'Agostino.

I asked all kinds of silly and important questions. What's the weather tomorrow? When is the next episode of "The Bachelorette"? How many licks to the center of a Tootsie Pop? Who sang "Brick House"? What are the directions to the New York Stock Exchange? What's Comcast's stock price? When's the next NBA finals game?

I asked the devices to spell words — like onomatopoeia. I asked to set reminders to call people. And then to actually call those people. I asked them to order me a pizza. I asked all kinds of questions, some that I cared about, and others that my producer, Betsy, really wanted to know.

Betsy Spring | CNBC

CNBC's Eric Chemi tests out personal assistant apps.

When it came down to accuracy, all the four apps could get the weather right, or find a stock price. But only one could tell me some of the harder answers, like who sang "Brick House" or when the next "Bachelorette" episode would air. The Google app, featuring Google Now's predictive power, was the winner here. (Intern Shane was simply a middleman, having to go through Google anyway to get me an answer).

When it came to speed, Siri, Google, and Cortana were all tied. These three for the most part could simply listen to what I said and practically immediately come back with an answer. Samsung S Voice was slow, almost as slow as the intern.

Finally, for ease of use, Siri and Google were the tops here. They most often gave the right answer on the first try without any additional steps. They didn't just dump me back to a big internet search that I'd have to sort through myself. It was nice to get a single answer directly.

Siri was the best at talking to me out loud, talking back to me as a response to my original command or question. That was ideal, rather than having to look at list of text on the screen. Siri was also the best at integrating the results into a specific answer on the Siri screen, rather than linking elsewhere.

Betsy Spring | CNBC

Personal assistant apps displayed on smartphones.

Other little things stuck out:

S Voice had a really weird creepy voice, so it was probably better to read the screen than listen to it talk. Here's an example:

Samsung hasn't yet responded to requests for comment about the creepy voice.

Microsoft's Cortana app had the smallest button, and my finger kept missing when I tried to click on it. The company didn't explain why the button is so small, but did say "we are also making Cortana more easily accessible, letting you interact with her even if your device is locked." Microsoft also said "we are always looking at ways to bring even more features/functionality to Cortana to help you get more done with less effort."

Siri's defaults weren't exciting: Bing for internet searches and Apple Maps for navigation. I would have preferred Google's services for those two tasks. Note that even the Cortana assistant avoided Bing, using a Google search instead. An Apple representative said Bing and Apple Maps are Siri's default options, and they can't be changed. The company also said Siri works with Wikipedia and Wolfram Alpha.

None of the four apps were effective at ordering me a pizza. The apps got lost in trying to make suggestions, giving me a list of restaurants to pick from. This was where intern Shane could truly shine, picking up the phone and actually ordering me a pizza.

CNBC's Betsy Spring contributed to this report.

This article has been updated to reflect that Google Now is one feature within the Google app, and to update the comments from Apple.