There's no real rule for what makes a good reference track. It’s up to you and your taste, but there are a few things to keep in mind:
Don't pick a track because you like the lyrics or because you love the synth melody. These qualities won't translate to your final master.
Use a track that has an overall frequency balance, stereo image, and level of dynamics that you want for your own master.
Use high quality file formats like WAV whenever possible. Avoid using lower bit-rate and lossy formats like MP3.