Since mid-2012, City of Ottawa councillor Doug Thompson has voted against the majority will of his peers only once*. On November 26, 2013 when Council debated the Transportation Master Plan an amendment was passed that modified the plan for Prince of Wales Drive. Thompson dissented.
You can listen to his reasoning in the embedded video (skip to 1h58m if it doesn't start there automatically). The details of the vote are available as well.
The frequency with which a councillor (or citizen commissioner) votes against the majority should not be considered a valid standalone measurement of their value. The job is about more than just voting. There is nothing wrong with being on the 'winning' side of every vote - it could simply mean a councillor is always getting their way.
Nonetheless, the minority report is interesting to look at if only to guess about why the variance in dissenting rate exists.
Among elected councillors, at the other end of the scale we find Councillor Rainer Bloess has dissented 3.38% of the time. Bloess is 15 times more likely to vote against the majority than Thompson. The transition from one end to the other other is also smooth, as you can see in the chart. Whatever factor influences how frequently a councillor will vote against the majority, the dose has been doled out smoothly from smallest to largest.
Here is a pretty chart. Open the Google document for a fullscreen view and to see the raw spreadsheet values.
Among citizen commissioners to the Transit Commissioner and Public Health Board we see a different story, though in fairness the sample size is smaller (they have fewer things to vote on in total).
Three commissioners, Johnson, Rahn, and Ferrabee have dissented on votes. Crew, Padolsky, Quinn, Reporter, and Smallwood never have (since mid-2012). For Ferrabee's one vote against the majority she joined Rahn and Johnson in voting against a security camera proposal for OCTranspo. The debate on that vote was interesting. Rahn has dissented twice, the second time by supporting Johnson's failed motion to have OCTranspo produce a non-peak on-time report. (Interestingly, Bloess joined them in that dissenting vote).
Johnson's outlier status as the only member with a dissenting rate above 4% comes as a result of his third and final vote against the majority. He voted against having OC Transpo annually review the bus advertising policy - a topic which spun out of the recent 9/11 Truther ads inside buses.
Being a relatively new member to the transit commission, Johnson has cast only 65 yes or no votes. Perhaps his dissenting rate will come back into range once he has more votes under his belt. Or maybe as a regular citizen, and younger than average committee member, he really is going to continue have a different view of things.
* OttWatch scrapes the voting history out of Ottawa.ca after meetings have concluded. It's possible some data is missing. (So perhaps Councillor Thompson has voted no on more than one occasion, but we missed that vote in the counting). Corrections welcome.