I think a comment editor is slightly more important. For my personally, I use SteemWorld to monitor the activity in regards to my account. Perhaps having a standard view and a raw view for comments, then a reply option.
I'm not really sure how often I would use posting of standard posts from SteemWorld. I guess that depends on how good the editor is.
But SteemWorld isn't currently a place you go to monitor your followed list. So it might not necessarily be where you are when you decide to make a post.
Ok, maybe I should explain my definition of a 'post editor' a bit more in detail :) From a developer's perspective a post can be a root post or a comment. Technically speaking the only difference is that a root post does not have a parent author/permlink. The blockchain only knows the 'comment' operation, which is also being used to broadcast a root post.
In short, it will be possible to write/edit comments with my Post Editor too and there will also come a feed view for navigating through different categories in the next few weeks ;)
It depends on how you do them. A comment editor doesn't necessarily have to be as advanced. You can start out with just a box and reply button. A post editor kinda has to have those quick links to make things bold and italic and such these days though. They are fundamentally the same in the back end, but one absolutely requires those annoying front end icon thingies and an image uploader, etc. A comment editor can likely be implemented first and then have features added to it.