Yep, My sacrilegious husband, a story of love, and Nativity, and action figures. Annie X-mas got me threadspotted for it! 
Searching for my answer to this thread definitely took me down memory lane, mostly for the better.
That said, I knew the answer right from the moment I read the OP. My most successful thread was Watershed Moments in SDMB History with 5 pages, 241 replies and 18,897 views. Phew!
After that is a Pit thread I now deeply regret (I was having a bad day and took out my anger on a hapless restaurant owner via the SDMB).
Reasonably successful threads that I am reasonably proud of:
I’m going to try to win back the girl (45 replies; 1,838 views)
What’s the deal with the Florida quarter? (51 replies; 903 views and inspired a fairly humorous discussion of lame state quarters)
Any Christian literature that’s actually, you know, good? (60 replies; 772 views)
Should schools require phys. ed. class? (56 replies, 830 views and inspired a pretty solid discussion about child health and the social pressures of gym class; maybe my favorite thread that I’ve started)
College professors say the darndest things
103 replies. 8510 views
Those 103 posts are dense with pleasurable reading, too I think. I did not really have any expectations for that thread since it was my first thread started in MPSIMS. I pleased with the results, but not really too surprised. Most of my threads are short GQ type threads.
Things I’ve learned about American homes from the movies with 105 replies is my top thread.
By the standards of the OP, Your animals aren’t your kids in The Pit.
I blinked and when I opened my eyes, it had 463 replies, 15,000 views, was locked, resulted in some dude getting banned, and contributed to (I think) one of the first accusations of “troll” (directed at me) after that rule was changed.
I started it just like I’d started a bunch of other pit threads (“this shit bugs me”) and have no idea why it caught on more than any other thread. Still, it’s far from a record in the pit. 10 page threads get going there every week.
The 2006 Weight Loss Club got 320 replies and over 5000 views, so it is the most popular on either account. I’m not too surprised at that.
Mine is probably this one:
“There is no God” is an opinion, not a fact.
It went on to 11 pages, but that’s because instead of reading what I actually was pitting, a few dopers (who are no longer here) turned it into a debate on the existance of God within about 10 posts.
I had a pretty strong inkling that my Tolkien trivia contest was gonna take off. It eventually went to 11 pages, with 502 replies and 5,370 views:
http://boards.straightdope.com/sdmb/showthread.php?t=366625&page=1&highlight=eldarion+tuna
Most of my threads go no longer than 10 replies or so, and some, alas, sink like stones.
Mine was What are the saddest songs you know? because I wasn’t feeling too happy that day. I pretty much figured it would go far since list threads of that sort in Cafe Society tend to at least go to page two, particularly when the topic is as universal as this one. I got 198 replies with 3,845 views.
Without searching all my threads (or posting a link because I don’t want that monster to lurch from its grave), I was shocked at the number of replies and the outpourings of vitriol in the Pit thread I started about some local restaurants threatening to cut off service to my (now former) employer if the employees didn’t start tipping better.
I think my very first thread, in reply to Cecil’s column on same-sex marriage, might have become a multi-page behemoth but there was some sort of data corruption in the thread which required it be locked, and somehow the replacement didn’t take off.
My top 2 both pertained to, um, traffic, :smack: with a thread about roundabouts vs traffic signals bein the winner.
Clearly I have a lot of deep stuff to contribute here. :o