Long term cell phone plan

Hello everyone,
I am starting my career in Japan next month, and I have quite a few questions about purchasing a smartphone:

1. Which carrier should I go with?
To my knowledge, there are 3 main cell phone carriers in Japan: Softbank, Au, and NTT Docomo. Which has the best data plan, and if there is a better alternative, please let me know.

2. Which smartphone with Andriod OS is the best? Or should I stay with Apple?
Right now, I have an Apple iPhone 6 Slim, but I do not like the way Apple does business, so I am greatly considering going with the alternative. Has anyone tried the Sharp Aquos line of smartphones? Are they worth the price? Are there any other worthy alternatives, or should I stay with Apple at the end of the day?

Thank you in advance.

If you will be travelling in Japan a lot, I recommend to get an Android phone because several, useful travel applications don't work on Apple phones because they lack the osaifu-keitai functionality, such as Mobile Suica (only useful in Eastern Japan), JAL touch&go and various payment services such as Edy. Also, I think Apple phones cannot be used to watch terrestrial TV which may or may not be relevant to you.

I myself am using arrows phones by Fujitsu. I love their battery life, but the camera is bad.

In addition to the three big carriers, there are also MVNOs which provide a no-frills service at a much lower cost. They have been discussed often here, so you can do a search.

Android vs. iOS... It's up to you, personally I find Android to be quite buggy and in general a much less pleasant experience than iOS, but that may be because I made the mistake of buying a Samsung phone. On the other hand, Android has osaifu-keitai, which I am heavily using (it has recently be made vailable for iPHones too, but it's not build into the phone so you have to use a special casing).

Mobile Suica (only useful in Eastern Japan)

Why only useful in Eastern Japan? It works elsewhere, as a card-type Suica does.

You are right that the Suica card functionality is useful nationwide, but the shinkansen reservation functionality (which I still doubt will become available on Iphones, but I am not sure), is only useful in Eastern Japan.

As a side remark, in 2017, a similar app for the Tokaido Shinkansen will be introduced. I am wondering whether it will be available for Iphone.

Yes, many features are only useful in the JR East area, but not all. In other areas, in addition to individual purchases (train rides, combinis, etc.), you can also

* Use the internet payments feature to pay for some online purchases (e.g., Amazon) with your Suica balance.
* Instead of using cash to charge it, have it charged on your cellphone bill (only available with the "big" carriers) or by direct bank transfer (from an account at a participating bank).

By the way, you can already use it to but Tokaido/Anyo Shinkansen tickets, however this requires registering your credit card, and I think only Japanese cards are allowed (the same goes if you want to use some of the JR East-specific features such as Shinkansen booking and commuter passes). http://www.jreast.co.jp/mobilesuica/use/ex-ic/index.html

After looking into it some more, it seems that the new service may not be based on a smart phone app, but rather by associating an IC card with a credit card:
http://jr-central.co.jp/news/release/_pdf/000029289.pdf

While we're at it, for the sake of Google here's a quick outline of Mobile Suica since it's not well documented in English:

It exists in two versions, an "Easy" one and the full one. The "Easy" version has fewer features, but does not require a credit card. The "full" version requires a credit card, and also has an annual membersip fee of 1,030 yen. I think only Japanese card are allowed. Also, the membership fee is waived if you use JR East's "View Card" credit card.

Like I said above, the "Easy" version has two additional features in addition to the normal features of a card-type Suica: paying for online purchases made at participating online merchants (notably Amazon, Yahoo, and Rakuten) and the ability to charge it through your phone bill (only at major carriers) or by direct debit to your bank account (only at Mizuho, Mitsubishi/UFJ, and Jibun). It cannot be used as a commuter pass, however, this requires the full version.

Of course, you can't insert your phone in the card slot of a ticket machine, so charging with cash can only be done at stores (e.g., combinis).

The full version allows charging it with your registered credit card, either manually or automatically when the balance reaches some threshold. It also allows "ticketless" bookings of

* Shinkansen of JR East (also the Hokkaido Shinkansen and the JR West part of the Hokuriku Shinkansen), with a discount of about 10% over regular prices;
* Green seats in some rapid trains around Tokyo (e.g., Tokaido and Utsunomiya lines);
* Tokaido/Sanyo Shinkansen, however this requires to also register to JR Central's EX-IC service;

and using it as a commuter pass. For all those things, payments are charged to your registered credit card, and not to your Suica balance.