Well, really it's a top 100 for Marvel, and top 100 for DC with a combined 200 count. That being said, X-23 ranked 36th on the Marvel list. Pretty high for a relatively new character that's only a little over 8 years old (she'll be celebrating her 9th year in 2012, and tenth year in 2013).
She beat many mainstays too in the final vote, from Black Panther, to the Human Torch(Johnny Storm), Invisible Woman(Sue Richards), Hank Pym, Black Widow, Vision and even the god of mischief himself Loki. She also beat fellow X-alumni Psylocke, Colossus, Cable, and Iceman. Her half-brother Daken is non-existant on the list as yet(update: he's listed at 91), so she beat him too by a wide margin. Laura's vote count gave her 470 points with 12 first place votes from the fan's company top 10 list each reader submitted for the poll.
When comparing her final vote tally's points to the DC side, she beat such DC mainstays as Lois Lane, Supergirl, Beast Boy, Donna Troy, Animal Man, and anyone else listed at 38th place or above. Sinestro creeps in at 475 to beat X-23 by a measly 5 points with only 2 first place votes.
If you're curious who else she beat on the CBR blog Comics Should Be Good's poll, head on over to the CSBG entry.