The Apple iPod nano is the top-rated MP3 player among critics. Most say it's easy to use, and they love the updated slim design. Audio quality is good, and video playback is impressive despite the small 2-inch screen. Apple has also added some new features like Genius playlists, shake-to-shuffle and a tilt-sensor screen. Be aware, however, that it's incompatible with some third-party accessories that worked with earlier-generation players.
According to your requirement plan for Mp3 or Mp4, I prefer to take MP4 when I am on journey so that I can enjoy both MP3 as well as Mp4 and when I sit idle in the room will prefer to listen mp3, there will be no big difference in terms of cost except you prefer to take branded ones, as per my knowledge having mp4 is good idea as it fulfills both your requirement..
Its your choice you want Mp3 or mp4.
In MP3 players you can listen only songs.
In MP4 players you can listen to songs as well as watch videos.Its
all upon you only.you want only music or music and video.
As Rajmi said both have their own sets of advanatge and disadvantage but as you said that MP4 Players have better quality music quality than MP3 player, that's wrong! MP3 players are better in music quality as you can only hear to MP3 songs. Mp4 players try to bundle evrything in a small player in a small which causes lack of performance.
So it is now your choice to choose which is better?
I know I can definitely tell the difference between a 44.1 KHz 192 Kbps mp3 and a 32 KHz 96 Kbps AAC mp4 at this point. Apple's own AAC encoder is probably in alpha or very early beta stage right now anyway.
I think I'll stick to my "lame --alt-preset extreme" encoded mp3s for now, even though AAC looks very promising indeed.