We are a long time user (Enterprise) with V6 installed alongside V5. We continue to use V5 for weekly mailouts to 800+ members of an industry association group.
We continue to use version 5 because we find the design philosophy in V6 too restrictive, so we continue to use clunky tables in V5. I had hoped that V6 would bring a WYSIWYG free format approach, but so far I'm not seeing that.
Personally I cannot stand the "I wanna look like Mailchimp" design approach. The fixed width and inflexible column widths are simply too limiting for what we want to achieve. (Correct me if I am wrong about the fixed width aspects).
Then there's the crazy behaviour when trying to stack images in a column. I've discussed this before and now accept I am probably too stupid to understand how it is intended to work.
It's a shame really. I see some compelling reasons to move to V6, but not being able to to the things we can in V5 are too discouraging and a deal breaker for us.
In the meantime, I hope version 5 will remain on the table,
My 2cents worth
Cheers