Spotify on best quality is 320kbps Vorbis (a patent-free alternative to MP3). It should be virtually indistinguishable from lossless for human ears (while using about 3 times less bandwidth / storage).

Here's a blind test comparing 128 kbps MP3, 320kbps MP3, and lossless. See if you can hear the difference ;-) Personally I can hear the difference between 128kbps and the rest most of the time, but not between 320kbps and lossless.

Note that Vorbis is slightly better than MP3 if I remember correctly, so if you can't hear the difference between lossless and 320kpbs MP3, you likely won't hear the difference between lossless and 320kpbs Vorbis either.