Allow sorting by fraction of comic read.
This sorting method would push the comics you are more interested in up to the top.
Number of remaining pages is okay when you're caught up, but when you have a lot of pages left, the ordering breaks appart. If you have one comic where you've read 100/300 pages, and one where you've read 2000/4000, the first one will appear first, because it the one with the fewest remaining pages, but it's clear to see that you're more interested in finishing thee second one.
An alternative could be number of read pages, I think it would be best to test both to see which works best.