3 > 2 > 1
This series got better with every entry. Crash Bandicoot 2 invented the slide mechanic and had very good level designs but Crash Bandicoot 3 was the one who invented the Super Powers (Death Tornado Spin, Super Double Jump...) which contributed in a way fantastic way to the gameplay. Besides that Crash Bandicoot 3 invented also the vehicle levels which are a fun variety to the gameplay. And Crash Bandicoot 3 had the best level designs imo (Egyptian / Arabian / Chinese settings were awesome).