In fanfiction I am primarily interested in well-drawn characters, strong writing, and interest-capturing plots.
I favor Original Characters over Canon Characters because with many of the canon Trek icons (most especially those of TOS) weíve seen nearly every aspect of their respective personalities explored and analyzed the canon movie/TV productions, the authorized novels, and in fanfiction itself.
And with canon characters, thereís really no sense of tension when theyíre placed in danger. Iím reasonably sure that Captain Kirk, or Commander Riker, or Major Kira arenít going to be killed during the course of a story. With original characters, the author is free to do whatever he/she pleases with characters of their own making, and very little (if anything) is out of bounds.
Ultimately, though, itís the characters and plot that draw me into a story, and itís the characters and plot that keep me there until the final page. The era the tale is set in, whether it takes place on a ship ship vs. outpost, these things donít matter nearly as much.