Plot is more important to me than character. Without a plot, there is no story. Without a story, what the heck are we doing? Character sketches are well and good, but I’m more interested in the voyage, not the people traveling with me.
That said, terrible characters can ruin a good plot, while interesting characters can totally save a horrible plot. You definitely need a good mix of both to have a successful story.
As a SF guy, I’m probably more tolerant of plot-driven, character-poor stories. If the story uses lots of
whiz-bang technology that bends (or breaks) the laws of physics, and those plot points are illustrated to me, the reader, via wooden, two-dimensional characters…I’ll still probably dig it. I’m in it for the pseudo-science as much as anything else. Other genres may not allow for the level of forgiveness I sometimes mete out to the books I read.
That said, the truly memorable, interesting, recommend-to-everyone-you-know stories are the ones
with whiz-bang technology wielded by kick-ass characters. So, Permutation City by Greg Egan manages to bend my noodle with its technology, but its characters are only “meh.” On the other hand, Altered Carbon by Richard K. Morgan manages to wed far-future tech with a hard-as-nails detective Takeshi Kovacs, and the combination results in a story I’ve shared with anyone that’ll listen. Likewise, John Scalzi’s Old Man’s War combines neato tech with a fascinating set of characters, and the final product is nearly perfect.
So, Plot comes first for me. But Character is almost as important, especially when you want to elevate a good story into a great story.