Depends what you want from it / if you know people there etc. 9th and 10th can be great - they're miles from most of the touristy spots but that's lovely imo. Canal Saint-Martin is a pretty solid bet for fun interesting food, galleries, shops, markets, nice walks along the canal etc. The 2nd is a bit fancier - the closer you get to the seine, the bigger and more ornate the architecture basically. All lovely though.
Depends what you want from it / if you know people there etc. 9th and 10th can be great - they're miles from most of the touristy spots but that's lovely imo. Canal Saint-Martin is a pretty solid bet for fun interesting food, galleries, shops, markets, nice walks along the canal etc. The 2nd is a bit fancier - the closer you get to the seine, the bigger and more ornate the architecture basically. All lovely though.