I have both and love both for different reasons.

The OP1 can create a lot of really awesome sounds and has really rad effects. The finger sequencer and endless sequencers are nice. I also like the 4 audio tracks you can put down and the album record ability.

The OPZ is what was missing from my OP1 experience. I honestly get so anxious when performing while trying to record that I feel like it takes me 6 takes. The OPZ makes it so I can quickly express what's in my head. The OPZ just transitions so nice. It also is awesome having so many patterns and projects on one device. I would get annoyed having 2 separate ideas on the OP1 and not being able to have a fluid work flow.

The OPZ helps me quickly sketch and honestly is a ton of fun. The synth engines are pretty versatile but not as great as the OP1.

If I were to try both for a month and choose one it would probably be the OPZ because of it's ability to quickly create.

After all, music is sound in timing