I doubt you'll get a 'what is best answer'.. What works for me, foobar2k(free), dBpoweramp(not free)..These work best for me!!. There are other ones, that no doubt work best for others.. That being said, "best" would be original lossless->lossy..And I'm not saying you'll be able to hear a difference when transcoding/converting from lossy->lossy.. To each their ears, uhh own!..
If you load the free trial for dBpoweramp it will continue to work after the 21 days last I checked. Last I checked it was 30 days so I may be out dated. A warning of caution. Transcoding, that is what you want to do, lossy audio may give you a quality loss. I suggest using Lame ABR if you must convert them. The main use of ABR mp3s is conversion from aac, wma and real media or any other of that type file. The other use is low bit rate audio books and podcasts. This again is because of the compatibility of the ABR to the commercial lossy formats. Try to approximate the same bit rate or go one better. ABR may pack a bit more quality than to others for the same bit rate. So if you are going from 128 maybe a 120 will probably fit. Fortunately you can do a clean conversion at 128 since that is a setting for Lame ABR. If you go for a normal mp3 (CBR) the mp3 will not sound very good at all. All the highs will be cut out of the music and will sound dead. Once converted don't convert them again! You shouldn't need to since everything plays mp3s.
