Although I am biased against anything Apple and iOS related, I'm going to be fair here.
I'm not going to mention standard smart phone hardware here (well mostly not going to mention) like camera, buttons, screen type.
I'm not going to mention Nokias, Windows OS or any other os out there with the exception of custom Android ROMS.
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iOS, iPhone and iPad -
Positives
. It's easy to use
. Much more apps and developers out there for the iOS which is great.
. Jailbreak - Although most casual users will have no need for this, when I was on iOS I had to have mine jailbroke, I hate the idea of not being in full control of my own devices.
. The phone design is simple has never changed much and comfortable in the hands.
. 3rd party accessories, have you seen the extent of these? Case, docks, pens it goes on and on, it is impressive.
. Cydia - I don't need to go into detail here, the apps and mods are amazing. Has a great community and great devs.
. Support from Apple in most cases seem to be positive and nearly every phone repair company handles iPhone repairs.
. unfortunately for me being an android user I have to admit to the fact the the App store for iOS is better, larger, organized better and easier to search.
Negatives
.Without Jailbreak it has always felt imo very locked down, not enough freedom to the device. Then again it has always felt that way with any Apple product I used.
. Flash support? This annoys me. There is none!
. Price, crazy dear.
. Ok so I am biased against iOS but seriously their fanboys/girls are terrible "OMG Android copied apple lockscreen notifications" or omg it looks like an iPhone! it's copying.... Apple were never the standard or the first to achieve most of their features, their whole take on Patents and copying is fucking pathetic.
. Without Cydia your homescreens and freedom to customize is limited to folder/app organisation and wallpaper changing.
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Android it's open source and many of it's devices
Positives
. A lot more depth and freedom to it's control.
. It has support from practically every other phone manufacturer out their.
. The Google Play Store, while maybe not as many as iOS but certainly a larger variety due to Live wallpapers, widgets, multiple apps to modify or change your phone experience (keyboards, root apps, themers, various launchers).
. Root, custom kernels, custom firmware, Cyanogen/MIUI , ok so there's way to many custom ROMS and kernels out their, specific to each device and many standard for multiple devices like the two I mentioned, root is practically gaining administrative rights which allows you to futher tune your phone, and install great root specific apps (titanium backup, root explorers, font changers, custom system apps). The custom kernels allow you to overclock/undervolt, tune volume, battery life, RAM consumption and much more.
. It's certainly a lot more tailored to the more advanced/moderate device users out there (in most cases)
. Jellybean (project butter) Androids latest firmware is incredibly smooth, has great transition animations, it's features are great and the Holo UI is pleasing to the eye.
. Various specifications, their is really an android phone out their for every users needs (unless your an iOS user obviously) Great camera phones, powerful phones, waterproof phones, large storage phones
. Most android phones support external memory and removable batteries.
. A lot of different manufacturers incorporate their own UI which of some are a standard or must have for some users, most notable that comes to mind is the Sense UI.
. Old android phones can get new life or latest firmware with custom firmware and custom kernels.
. Ubuntu OS - have you seen this thing? SEXY!
. With custom roms and Recoverys you can always just go back to stock from a back up you make through Recoveries or a rom manager app and vice versa.
. XDA developers website/forum - what a site it is. (just check it)
Negatives
. Ok so widgets, live wallpapers and heavy RAM usage apps drain the battery like a mother fucker and can slow the phone down.
. (This ties in with the first negative) - Users complain who complain about crap battery or freezing/crashing are usually those who run seventy different apps/widgets at once or mess about with the phone in ways they either shouldn't be doing or don't understand.
. Some network providers and phone manufacturers are really heavy on their own corporate apps (bloatware) which is incredibly annoying, luckily root access = deletion of said apps.
. The vast phone variation can be somewhat annoying with certain phones only supporting LTE or lower specs at same price compared to others, not supporting some phone carriers, not sold in certain countries or banned due to patent wars.
. Accessories are limited - Many users love phone cases and accessories (making their phone more personal to them or making it look more appealing) unfortunately some android phones have very few accessories/cases, luckily AUX cables/ Micro USB has much support.
. Slow updates/ Bug fixing is slow - Ok so this not may be the case with some devices but I'm sure you've all seen stories about how AT&T or Verizon take weeks or months after an update has been pushed because they need to tune it to their crappy bloatware and carrier standards (just using them two as an example) Phone manufacturers are also the same.
. Inevitably old phones don't support or have latest updates for the latest firmware, or some phones which could support it don't get it.
. Pirates! Fucking pirates everywhere, android certainly has a larger pirate community unfortunately.
. Malware/Adware/bloatware - Dodgy apps, apps with crazy permissions - Be careful when downloading apps not from the Google Play Store and in some cases some apps from the Store they can do many things you might not want them to, check the permissions, make sure it's legit, do some research if your installing weird 3rd party apps.
. Ice Cream Sandwich has flaws, avoid it.
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Other things to consider
1.You can perma brick most smart phones, if your going to tinker with it, make sure you know what your doing.
2. App availability, their are specific iOS apps I like and specific Android apps I like, if it's down to what apps/games are available to you, make sure you do the research.
3. Don't go with iOS just because it's Apple, try other things if your not completely against Android.
4. Ad's , ad's everywhere - Install an adblocker.
5. Don't change if you don't want to, stick to what your comfortable with but at the same time take a look in shops try out different phones that catch your eye.
6. In android their is certainly a lot more positive, but also great amount of negatives.
7. In part their isn't an incredible amount of things that any android device can't do that iOS can do and vice versa.
8. If your reading reviews about any technology or softwate, check the date, alot of them and I mean a lot of them for iOS and android are outdated or are talking about old software. iOS 6 and Jellybean are not the crappy software they were 1-3 years ago ios 3/4 - Android 2/2.1 / 4.0
9. The little things, don't forget to really take a grasp of all Android/iOS has to offer it's the little features that can make a phone or software stand out sometimes.
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Why do I pick android:
I had iOS and I wasn't happy with it, ok so some of the iOS only apps/games are nice but I don't really care about that, I'm currently using a Nexus 4 and it's speed compared to the iOS is no contest. Anything I used on iOS I can get on android.
I have so much more freedom with it and it's cases are decent, dev support is amazing and it's specs for it's price are great.
I just over all have a more pleasent experience with it's software, it's hardware, it's mods, the community.
If your an iOS fan read this, if considering to jump of the Apple zombie train and board the Android nerd band.
http://gizmodo.com/5933636/an-openly-biased-review-of-android-jelly-bean-by-an-iphone-lover