"Best" is relative but I'm a big fan of cuetools/cueripper
It handles Flac and quite a few other codecs with different back ends, does accurate rips and checks the rips against a DB. Its portableish (needs .net but no install) - so testing to see if it meets your needs would be pretty painless.
Windows' own built-in Media Player can rip CDs to WAV or AIFF - which is "original quality" 16-bit 44.1kHZ uncompressed, as well as to MP3 etc.
It's not open-source, but it's free ;)
After that you can convert to any format you like. For quality vs size, I'd recommend AAC over MP3, AAC can be lossy or lossless, just like FLAC, but has wider ...