I use both a Nook Color and iPad 2 for reading manga. I have CM7 installed on a Sandisk 16GB microSDHC on the Nook Color and use the
Perfect Viewer app which is pretty decent. On the iPad 2, I use Comic Glass as my manga reader. Both can read rar, zip, cbz and cbr files just fine - no need to convert or extract. Both also have options for right-to-left reading and splitting double-page spreads.
Between these two apps, I prefer Comic Glass over Perfect Viewer. However, I do find the smaller size of the NC make it much more comfortable to use for long periods of time compared to the iPad. I actually find text to be crisper on the NC compared to the iPad, likely owing to higher pixel density. Alas, the iPad has much longer battery life compared to the NC. Still, battery life on the NC is pretty decent. I get around 4~6 hours of reading time on a single charge. It just so happens the iPad has crazy good battery life for a tablet (more than 10 hours).