Just got my I9505 black mist 16GB S4 today to replace my HTC Desire HD which has been feeling a bit long in the tooth with its quaint single core processor.
I'm not bothered about only 16GB because I think that 2GB RAM + 16GB internal storage + up to 64GB SD card storage = plenty to do whatever.
This S4 definitely blows away my old Desire HD, many things are noticeably faster, the sound is much better the screen is stunningly superior and the extra features will be nice to play with.
I've already setup the IR Blaster to control the TV so I never need to worry about where the remote has been put.
When I powered up the phone and gave it the details of my Google account I got all my contacts, E-Mail, calendar and apps - so very easy!
I had used SMS backup on the Desire HD and once it had installed on the S4 I did a restore and got all my SMS texts onto this new phone.
Right now I've just put in my old 16GB SD card but I'll get a new 64GB card in the next few weeks so that I don't run out of room when using the 13mpix camera.
The internal storage can hold my apps and I'll use the SD card for music, books, movies & TV videos, photos and output from the camera app.