Put very simply, high bitrate MP3s are where you copy your CDs to the computer and the audio is converted in a higher-quality MP3 file.
MP3 is a lossy compression method where the audio can loose quality depending on the level of compression and the encoder employed. In MP3 terms, the higher the bitrate, the better the quality will be (whether you notice it, particuarly in a car or other noisy environment is a different matter). The downside is that the files are bigger.
MP3 bit rates for copying music tracks in most audio programs can be set from 64Kbps to as high as 320Kbps. The higher the bit rate the more audio precision is maintained within the compressed file.
So MP3 players that can handle MP3 files with high bit-rates are favourable if you prefer to have high-quality audio files rather than just cramming as many MP3s as possible on there.
I have a 4GB Apple iPod Nano which is very easy to use. The only thing with iPods as you may well know is that iTunes is the only audio application which can be used to manage the iPod.
All the same, I like iTunes and I use the Apple Lossless Encoder for my music. A lossless encoder means that the audio quality should be the same as that of the original on the CD. The downside is that the files are 30Mb to 50Mb per track depending on length and the variable bit rate.