Depends on the topic.
Generally, the Terry Lee textbook is more difficult. However, some questions are irrelevant to the HSC and thus appear difficult not because of the difficulty, but because of the lack of exposure.
For example, the syllabus strictly states that locus problems to do with the ellipse are not required, but his book has quite a lot of difficult locus problems.
As for HSC style, that's a hard claim to make. The style of the HSC is changing, and has always been changing. There are now a lot more proof questions as opposed to calculations, and his book has a substantial number of calculation questions. Also, you may notice that in recent HSC questions, there have been a lot of "Prove that AB x CD = EF^2" kind of questions, but there are very few of them in his book.
On the other hand, the Coroneos book has MANY of these types of questions (more than 10 iirc) and essentially every single past conics question in the HSC is also in his book.
But tl;dr the answer is Terry Lee.