Quite frankly, implementing WYSIWYG editors (and choosing the right one) for Drupal websites has been a pain in the ass the past few years. For a while I bounced between FCK and TinyMCE - both integrated in the right fields fine and played well with IMCE for image uploads, but I remember finding their markup dirty (lotsa br tags etc..) and clients getting quite confused with line breaks in the editor not being truly mirrored on live content. Of course, some of this is due to configuring Input Formats properly, but then there's also general interface and aesthetic issues with those mentioned editors.
Recently I've begun implementing HTMLbox on a bunch of sites - its simple, seems to markup html pretty well, and affords site users the basic buttons for simple formatting and link embeds [look out for a more in-depth review soon]. However, one downfall with it is a reliance on IMCE for facilitating embedded image uploads. For anyone who's ever used IMCE, you'll know how confusing it can be for anyone unfamiliar with inline editing - though it integrates with the editor, its interface is still seperate and requires a lot of styling effort to pretty it up etc...
So, though HTMLbox is pretty nice, I've really been looking for an editor which installs light and easy *and* offers the ability to upload images inline - whilst editing a piece of content. Added bonuses are future scalability and options for extending editor functionality to include things like seamless Flickr image and Youtube video embeds. Guess what? I found all that in YUI Editor - a module for Drupal which lets you use the Yahoo User Interface Editor within your own site. I highly recommend installing it and playing around; you'll be using it in no time and find that all the basic functions are there... though as Nick Lewis recently blogged, there are downsides with this Drupal implementation limiting the extensibility of the editor.
Personally, I love the embedded image handling with YUI Editor but hate how it offers a very basic, Wordpress-esque, feature set - ultimately, there is no imagecache-style on-the-fly image sizing/thumbnailing, rotation etc... However, as you'll be using the YUI module in order for the Editor to work, your sites can now benefit from other Yahoo User Interface widgets like their Calendar and html button override.
(Written by Qasim - Principal/Founder @ Design Guru)