I like Comic Rack because of the front end interface and how it handles the individual comics, it also seems faster than PV alot of the time for me.
Do you mean page turns are faster? I'm testing them side by side on both the Nook Color and the Nook HD+, and there is a noticeable pause between touch and pageturn in Comic Rack, whereas in Perfect Viewer it's basically instantaneous. From fresh installs on a (currently) CM7 Nook Color, Comic Rack did have my library loaded pretty much instantly and automatically whereas PV had to be pointed to the folder and then did a lengthy scan. From then on, though, PV just beats the pants off CR for loading times and page turns.
It's all moot if you're planning to use the stock reader, but I figured I'd do the side-by-side since both devices were handy.
I just played around with the HD+ stock reader some more, and it's a little weird; the first CBZ I tried last week originally appeared under My Files in the Library app, but ended up shelved under Magazines after I'd opened it. I just tried loading several issues from a series to see if they'd be listed as a series under Magazines, but they didn't get added to the Magazine shelf. They show up in the Recent carousel, but to get at them via the Library I'd still have to go through My Files. The only change I've made was to change the folder name from /ext_sdcard/Books to /ext_sdcard/Comics. I'll mess around some more and report back.
ETA: Somehow the comic I opened last week ended up in /sdcard/My Files/Magazines, and as such shows up under Magazines in the Library. Some CBZs do have some odd artifacting at the bottom of the page, like the bottom few pixels were smeared down the page.