Which kind of undergraduate course is better for a student wishing to do research in physics?
The most important thing is to follow a course where you'll be stimulated, have access to good people and good resources, and be happy (personally, not just academically). If satisfying these conditions also determines which style of course you follow, then that's the best answer.

Otherwise... there's probably no definitive answer. Personally, I'm in favour of a broad scientific education. A lot of interesting developments these days are at the interface between two or more of the "traditional" sciences, and being able to bring in ideas from multiple fields is often useful in research. There's also the fact that you may find your interests don't (only) lie where you thought. My career has ended up being in a branch of science I never even considered when I was at school (I, too, wanted to do theoretical physics).

Choose a course that will give you a strong grounding in mathematics: it is probably the only part of a course that's guaranteed to be useful wherever your career goes. (I took advanced courses in particle physics... but I haven't used that knowledge since leaving the exam. Introductory linear algebra? Almost every day...)

In support of my position: note that some of the world's leading universities (eg CalTech, Cambridge) insist their students study multiple traditional sciences.