I consider the iPod Touch an option mostly for music. Recently, I purchased a used 120GB iPod Classic because I wanted to have a majority of my music library on the go. The iPod Touch offers this same option nowadays with up to date music player options and Bluetooth (holy hell did it dawn on me how much I use it when my Classic didn't even have the feature).
As others have said in this thread, the experience is admittedly something that stands out from competitors. I did lots of research before purchasing my iPod Classic and there really wasn't anything that really came close to it in terms of all around convenience. In terms of storage, Android devices with external storage are technically up to par and even surpass it with flash storage, but audio quality and dependability leave something to be desired. I've found it a little sad that the audio output quality on the Classic outperformed the one on my One Plus One for example. Admittedly, there are EQ apps that can remedy the situation, but in my experience, DSP managers on Android have been somewhat hit and miss with the audio mods inexplicably not working sometimes. I've been hard-pressed to find dedicated music players that bring the best audio quality coupled with a good user experience, which i-devices excel at. The Sony Walkman is perhaps the best rival in this regard, but don't even get me started on it's price. Between the Walkman and an iPod Touch, the Apple devices wins hands down in two very crucial categories; it runs an up to date OS (iOS 8 vs Android 2.2) and is better-priced.
Moving on, iTunes and i-devices' compatibility with each other is one of the few things I think Apple can still be proud of these days; syncing media has never been easier on any other platform, in my experience. Part of the reason is thanks to the way iTunes indexes your music, making it easy to browse and also access the files directly if needed for Android (but you're missing out on automatic sync and other features this way). It's such a breeze to add songs to my iPod by just adding them to a playlist any time before I want to sync it, plug the iPod in and let the magic happen.
In conclusion, the only pro IMO to going away from Apple for music is expandable storage. But if you're looking to get a device that has expandable storage, a good user experience and good audio quality, be prepared to shell out just as much as, if not more than, an iPod Touch.
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Regarding the argument of going all out on an Android phone and using it for everything to save from carrying two devices, battery life becomes a major issue. I think that having a phone for just that and another devices for all your multimedia/Internet needs is ideal. With data, how much do you really use the "phone" components of your smartphone? Text-messaging is almost obsolete and there isn't really any essential interaction between the actual phone component of the modern smartphone and apps.
EDIT: Just as an example, I recently accidentally got myself in this exact situation with two phone plans (one with just talk and text and the other with unlimited data) and it has actually been great. Ironically, I've been using my One Plus One for all the features I said I'd use an iPod Touch for and an iPhone 4 as just a phone (mainly because I made myself essentially go broke on buying camera stuff), but I think my point about what to use devices for still stands.