Well, just to offer a different opinion. I currently use a Samsung Note II. While, it's much larger than the S3 and S4 the feature set is relatively the same. Plus, I've extensively demoed the S4 (Girlfriend owns one) as I was going to upgrade to the device.
When it comes to media, it all can be done via drag and drop straight to your on-device storage or an SD card. I personally use Spotify premium as it allows for offline playing of your playlists.
As for the Galaxy handsets having "Little usable" space, I'd have to disagree. Much like other handsets these days, they come in the 8,16,32GB variations. So, it wouldn't be any different than they're apple counterpart. If anything, I've actually notice IOS uses a little more space than the average android install.
In regards to size and comfort, that's all something that varies with each person. But, I'll say that the S4 does fit well in your pocket and operates with 1 hand very easily. Couple with ease of use and the versatile customization options that come with android. I'd say the S4 would be a pretty good candidate.