Siri vs Cortana.which is better?

I think that windows phone has finally reached a point where it can compete with Siri and even Google now.
I've used Cortana and Google now but as I have never used an iPhone. So will you please explain which personal assistant is better and why?(personally Cortana takes care of every query of mine).
Please give unbiased answers.

All three assistants are very comparable, however I will state that Cortana is currenly in BETA. It's full potential has yet to be released. With that in mind, given that Cortana can (even in BETA) compete fully with Siri and Google Now on many issues, it's kind of hard not to want to grant "winner" status to Cortana. I'm using the Nokia Lumia Icon with WP8.1 Developer's Preview and can honestly say that I'm EXTREMELY impressed with Windows Phone and Cortana. I switched to WP8 (Nokia 928) after having my Samsung Galaxy Nexus and am still using my Nexus 7 tablet for the few apps that I don't have on WP8.1. Honestly though, as more and more apps appear in the Windows Store, I find myself using the Nexus 7 less and less. Since the Nexus 7 is a "Nexus device", I currently am using Android 4.4.2 and find it to be very "laggy". My friend on AT&T has a Nokia Lumia 925 and has also upgraded to the Developer's Preview. We have compared his 925 to my Icon and my Icon is a little faster than his at most things, but not many. The point is that Android upgrades slow down older devices. Windows Phone 8.1 works just about as well on an older 925 as it does on a newer Icon. So the only advantage to getting a newer Windows Phone is the better camera, more microphones, etc. Basically HARDWARE. Software wise, WP8.1 works PERFECTLY on All Windows Phones. No lag, no freezes, no restarts. This is the reason Google will not make apps for Windows Phone. They know that if they do, their laggy, unstable Android OS is done for.

As far iOS7, it too runs slower on my old iPhone 4. Apple even admits this and supposedly they are trying to work on a "fix" for this, but so far… Also remember that Apple doesn't have it's own search engine. Siri gets its information from Bing Search (Microsoft) and Wolfram Alpha. So, it can't keep track of your interests the way Google Now (Google Search) and Cortana (Bing Search) can. Google tracks EVERYTHING you do with no way to prevent it. Cortana has a notebook that you can tell it what it is allowed to keep track of and what not to.

I'm trying my best to be "unbiased", but given the above, it's kinda hard not to lean towards Cortana.

You can use any search engine to find several reviews that have already been done comparing Cortana and Siri and Now. Most will tell you that Siri is good for some things, Now is good for other things, and Cortana is good at both things.

I've never used Siri, although several of my coworkers use it. I have used Now, and Cortana (Nokia 1520 w/preview WP 8.1) and Cortana is impressive. The only issues I've had with it so far have been caused by noisy environments, not the software. The ability to operate almost all functions of my phone using my Bluetooth headset is what I wanted, something that Android has consistently failed to do for me. Other than to use the camera or surf the web, I don't have to pull my phone out at all.

I watched a show named Gadget guru and in it Cortana was really better from siri and google now

Well right now, its not fair to give an answer since Cortana is still in beta as well as Windows Phone 8.1, vs Siri which has been out for some time now as well as iOS 7.1.1.

Though from what I have seen both have their +s & -s so I'd say they are just about equal.

As far as WP being now a good third option, that's jumping the gun a little. There's still the problem with the lack of apps vs iOS & Android.

All the other answers are super long and I don't do that. My answer is Siri.