For quite some time I've used CDisplay but once I've seen PicWalker and then MMCE I switched to them. I was trying at least a dozen different comic viewers but none of them was as good as MM or PW.
PicWalker is much smaller and uses less resources than CDisplay while at the same time has more options and Manga Meeya and PicWalker let you read more comfortably (the continuous pages option that I've mentioned about, if someone has never seen it he won't know how much better reading manga can become). MM and PW have smooth scrolling, not jumpy one as in CDisplay, which combined with continuous pages makes it perfect for viewing manga. MM and PW have thumbnails options which you can easily configure (especially in MM 7.4). MM has very advanced zoom function which is even better than in Photoshop (I'm not kidding, the lanczos filter I as talking about. Thanks to that even LQ scans can be fit to width and you'll be able to read what's written in a small font). In MM and PW you can easily save/copy pages. Both have built in graphic editor which CDisplay doesn't have and CDisplayEx has but is less advanced. You can do most of editing without using Gimp or PS. PicWalker has option of batch convert of files, e.g. if we have 1000 .png files and we would like to convert them to .jpg files it's no problem. You can customize key/mouse configuration as you like in both. PW can find duplicate files (which can be very useful when someone has thousands of Claymore images for example: http://www.megaupload.com/?d=FAM6MBV2
). Both MM and PW have slideshow option which you can configure as you like (so program scrolls for you). Both have "Favorites option" and you can bookmark where you left off (in PicWalker surprisingly it's better done than in MM even though it's much older and you can bookmark dozens of files) so that you will easily access the exact page of the exact file you want. They both have the hitory of recently opened files, e.g. last seen file was Berserk chapter 288 and after running the program it starts with that file (it depends on how you configure the program, it can do that or not). But what's even better it remembers exact pages of previous files, so if earlier I was on page 123 of Claymore volume 12 and I'll choose Claymore volume 12 it will go there (you can configure that also) !!! Which is really, really convenient. There are plugins (especially for MM, for PicWalker they're hard to find now) and skins. Like I said earlier, it can easily access archives in archives (or even archives in archives in archives, etc.). Installation isn't needed. It has also continuous pages modewhich is the main reason I loved these programs.