I constructed two "disagreement with PAP" indices using data from Electionaire, which rates each party's position on 15 topics, from inequality to ministerial salaries, and scaled them on a range from 0 to 5. Read more about the questions and findings.
In the first index, I took the simple difference between the opposition party's and PAP's responses, and averaged the differences by party. All 15 questions were used, although some parties had no view on some issues. As the blue bar in the chart below shows, SDP and RP scored the highest on the disagreement index.
In the second index, I conducted principal components analysis (PCA) on 13 questions, omitting questions on homosexuality and racial quotas in HDB flats due to missing answers from some parties. The purpose of PCA is to measure the "underlying" stance or motivations of each party. The findings here are again very similar, with SDP and RP coming up tops again.