Should i buy an iphone 5 or xperia z ultra now?

Please, don't give one line answers (like X is way Better than Y as that would just increase my confusion).
My birthday is next week and I was thinking of The iPhone 5 or xperia z ultra, I'm used to huge phones (I currently have Galaxy Note N7000). Don't suggest, Galaxy S4 or LG Phones as I prefer high quality phones over plastic phones. I don't care how much power is there in Galaxy S4, my girlfriend just got it and it has lagged atleast 5 times in the 4-5 hours I have used it. Basically, as the next iphone should launch pretty soon, should I go for xperia z ultrat? But, wouldnt it be very huge. Also, wouldnt the next iPhone be almost identical to this one.

Additional Details
Also, if it helps, I have an iPad 4th Generation and Alienware M15X. No Macbooks or Macs as I prefer Windows due to the fact that almost my whole life I have used windows 98, xp, vista and 7. I did use one macbook pro when I was studying in MIT(around end 2010), but I switched back to windows almost two - three months later.

I've heard a lot of people complain about the iPhone 5

If you prefer big screens go with Xperia Z.
If you prefer high quality phones as in resistant phones go with Iphone 5.

I Say The iPhone 5.It's Great iHave It & No problems Yet Ha.

I'd prefer to buy the next iPhone instead of these two.

I wouldn't buy anything before the next iphone came out and that's expected early next month. Nobody can be sure whether it will be a good phone.

I'd say get the galaxy mega for 5 reasons. You get almost the same size. You get a decent specs. You'll get the same drool from people. You pay 1/3 of the price and finally. You'll get a headset in the box. I studied both ultra and mega for two weeks reading all reviews and got a mega. It has a brighter screen and pre installed features than the ultra. For 30, 490 net ultra why did they take the dock and the headset for Christ sake. It feels like you're being robbed getting the ultra without it. I bought a mega with its complete accs in the box. Sony must look into this cause cause I'm really poised in getting the ultra that day.

If this question was asked 1 month back, then I would have suggested you to buy iphone 5.
Now we have seen the fastest processor of all the mobile phones in Xperia Z ultra.

Amazing picture quality with Triluminos with x-reality.
This fits perfectly in between phone and tablet- A Phablet!
Superb built quality and sexy style.
Good choice of colours.
Screen Mirroring- for easy sharing of photos and contents with Sony Bravia
DLNA-
New I phone series are not coming with similar size range.
Hence I strongly suggests you to buy Sony Xperia Z now. The same Japanese brand who was know to be the best in quality…

Size wise- Yea its huge, Dimension-179.00 x 92.00 x 6.50, but it serves the purpose of a tablet or laptop to a certain extent.
Con- Battery can run for full day only & Non removable, lack of flash.