The best I have found for general use is Audacity, a freeware audio editor. I have used it to transfer about 50 LP records, 20 cassette tapes and 2 reel to reel tapes to CD's and to MP3 format

. You can record a whole tape track/record in one go then split it into single tracks and rearrange as you please, it has noise reduction so you can edit out tape hiss etc:
I had some old Mono tapes/records and after editing I copied the track to another track and made it stereo - same track but plays through both speakers and sounds a lot better.
Download it at: audacity.sourceforge.net/
Download the MP3 converter whilst you are there and you will be able to save directly to MP3 Format