Commerce 1 or Commerce 2?
As @No Sssweat points out in a comment on your original post, there is no Commerce 1 for Drupal 8, so if you're upgrading your site to Drupal 8, Commerce 2 is your only option.

But even if that weren't the case, Commerce 2 is stable and it's where all the current improvements in Commerce are happening. While Commerce 1 may have a larger contrib ecosystem at present, I find that once developer energy has moved on to the latest version of Drupal, it's frustrating to try and solve contrib problems on the old version. So my advice is always to go with the more recent version, once contrib has progressed enough that they key functionality you need has been developed and is reasonably stable. I believe Commerce 2 is there.

Finally, the migration process is kind of a bear (especially if you're migrating historical order data), so personally I'd only want to do that once, D7 Ubercart directly to D8 Commerce 2, rather than the two step process of D7 UC -> D7 Commerce 1 -> D8 Commerce 2. I think you'd be creating a lot of extra work for yourself without much benefit.