I consider my LJ my "primary" journal and DW my "back-up" journal, but I'm leaving comments enabled both places for the convenience of people who'd rather comment at DW. For ease of management I'd prefer comments on LJ if you read both places.
I've also imported all previous comments to my posts over to DW, and may continue to do so in the future (I don't know if they have a good way to keep comments synced currently, but I want to also cover the possibility that I'll choose to do so in some manual way or to do so automatically if a good way presents itself). These comments are in the context of the posts on which they were made, and with equivalent security levels (those in locked posts are still in locked posts, those in friends-grouped posts still in groups with similar purposes and criteria for group membership), so it feels like an appropriate way to "archive" them as part of my overall journal. However, I realize that some of you may feel differently, and I want to respect that.
If you don't want your comments to my old posts in LJ appearing over on DW, I will go through and screen them for you. This is not an automated process and will be a pain in the ass for me, so please only ask if it's important to you. They show as being made with your LJ account using OpenId, and you are also able to go through and delete them yourself using that OpenID login on DW.
If you have a DW account and would like to be added over there, please comment on this post both places (noting the different usernames in both posts if you don't have the same one). That makes it easy for me to click the little userheads on each comment and get you in the same security groups. (There no automated way I have found to say "this DW user should have exactly the same privileges as this LJ OpenID account, so add them to those imported security groups" so I've been opening that page side-by side and adding them by hand.)
This post is also available at http://algeh.dreamwidth.org/275490.html. There are currently comments there. Feel free to comment in either location.