This one was my first mp4, about -> https://techmallcr.com/images/productos/NWZ-S615.jpg
At the moment, I have an iPod Nano and it's pretty awesome. I didn't really had the need to change, but I always wanted to have an iPod. Very simple to handle, it's pretty, the only problem is that you can only sychronize with one computer. This means that if you go to a friends place, you can't give him your songs. That's really the only problem, I love the rest about it.
If you're not very into the whole "ipods" thing, I'd advise you to check this one: http://www.sony.co.uk/product/nws-e-series/nwz-e455