Yes, all of them. I know that’s not what you wanted to hear, but do read on…
Start with the easy ones, then move on the medium ones, then move on to the hard ones.
Intro (and advanced) physics is not about learning how to solve specific problems, so you can solve them again on a test. It’s about learning general concepts so that you can apply them to specific (and new) situations when they arise, in what ever field you are working in.
By calling out specific problems from a text, or giving out old exams to study from, a student can make the false, and usually detrimental assumption that the future test will simply be a re-hashing of these ‘specific problems’. The top scores on any given exam will be given to those who can demonstrate they have learned how to approach a new situation, using the frameworks and concepts you have been studying.
This doesn’t mean you should not practice doing problems. You should absolutely practice doing problems, but just not with the expectation that you will see the same one again on a test. By practicing problems, you will learn the general strategies and methods that are necessary to solve something hitherto unseen.
As an analogy, consider learning a foreign language. Maybe in the very beginning, a test might include a list of vocabulary words that you will have had to memorize. However, soon after that, it will involve translating and understanding new sentences and phrases you have not encountered directly before. Being able to do that is what it means to learn a language. Physics is no different. Instead of words, we have basic (and small in our case) equations and variables that you need to master. Then you can express your fluency by using them to describe the world.
The same would be true of sports, for example, baseball. You practice certain things over and over, but when it comes to game time, you don’t expect to see the same exact plays you did in practice. There will always be new actions you will have to figure out how to deal with. And so, in practice, you try to expose yourself to many different possible situations, but all the while, you know you will likely see something different during an actual game. This is what a good ball player can handle.
So, to summarize, when studying physics, solve as many different problems as you can before the exam. This will strengthen your overall physics skill set. However, make sure you are not simply memorizing the steps for a certain subset of problems in the hopes that an exam will just ask you to repeat those same steps, exactly. That’s not physics. True physics work involves being able to absorb a new situation, and then apply the abstract concepts you have hopefully mastered.