Some are say, 2249 and the same song can be 4449. What is the difference?

Different Bitrates.. The higher the bit rate the better the sound quality, AND the bigger the file size. You can view bitrate in the search window by right clicking on the title bar of the column and selecting Audio > bitrate.

Sometimes songs are uploaded incomplete as well which is a pita then the files will be smaller

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To get Phex Click on the Fox

I just downloaded the same song with different sizes. It seems like the quality is the same and the song is the same size though.

A song with a bit rate of 128 kbps might be 3MB size The same song (same lenth) with 256 kbps will be 6MB it will sound the same on my computer playing through its single poor quality speaker. If you play it through a decent stereo and/or analyze the compresseion etc, you will find that the higher bit rate will give higher quality sound. A shop bought CD will give better sound than either .. It all depends how much of a hi-fi buff you are. I guess

What more can I say?

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To get Phex Click on the Fox

Great, so I will look for the higher bitrates by hitting Bitrate and the bigger numbers will got to the top of the list then I can choose from here so I see.

Sometimes the songs don't sort exactly by bitrate, you might get some very small bitrates appearing first...just ignore these! Yes, go for the higher bitrate. (It still pays to preview them) I'd ignore anything lower than 128.