International Relations student here
I can confirm the courses are nearly identical; the only things that differ are some of our core and compulsory modules (to exemplify, as a first year student, I had to take Introduction to International Relations and Politics students had to take Introduction to Politics while Politics and International Relations students had to take both), and even then, an International Relations student can pick the core and compulsory modules of a Politics student and vice versa. You can definitely find a Politics student and an International Relations student who take the very same modules, but who get different degree titles based on what their core and compulsory modules were.
When it comes to career opportunities, it makes no difference whether you take Politics, International Relations or Politics and International Relations. Sure, the content differs slightly (Politics modules focus on a national scale and International Relations modules focus on a global scale), but they are still so related that most people think of them as interchangeable. At the end of the day, we are all politics students; we just focus on different branches of politics! Obviously, a Politics degree tends to prepare you for a career in the government better and an International Relations degree tends to prepare you for a career in international organisations better, but that is not a rule since how prepared you are for a career in those areas depends way more on the modules you study, transferrable skills and work experience.
Think of what parts of politics you are most interested in. Are you more passionate about local/national politics (e.g. political parties, elections, the government, policy, political journalism) or global politics (e.g. war, terrorism, international organisations, peacebuilding, international development)? If you have no strong preference, take both or either (see what university has modules that interest you). If you discover you have a relatively strong preference, pick the one that best fits your interests.
In my case, I do not care about political parties and national politics, but I am extremely fascinated by everything related to international relations, so I picked International Relations in the end
Even if you do have a preference, you can still take the other or both and simply pick the modules that interest you. I could definitely have applied for Politics or Politics and International Relations courses and I would still have been happy with my modules, because even when some module titles are different, the content is the same and just used in a different (national/international) context. What matters most is the modules that the universities you apply for offer and how much you would enjoy studying them.
To summarise, there is no 'better' one to pick. The differences are minimal and can be further minimised through optional modules. Just choose a course which you believe you would enjoy more, regardless of whether its title is Politics, International Relations or Politics and International Relations.