Is it better to branch in something not similar to your civilian job?

If you are earnestly jonesin' to be a cop, then I would go with MP. Military-grade law enforcement training (i.e. directly applicable experience complementing your resume, which very well may come in handy when you are up for Detective/Sergeant, Capt., etc....I smell a pay raise). The synergy of civilian and military training - plus your developing experience - will undoubtedly enable you to not only be a better cop, but also to be even more respected within your department and community. I imagine the more inclusive experience might also bring you much more palpable job fulfillment, benefits, and a STRONG NETWORK that can attest to your skills (i.e. personal branding, accolades, letters of recommendation, trust, hot dates with a huge uniform fetish....and so on).

As far as I can see, the downsides are the potential burn-out from dealing with bullshit (on the beat and in the office), and personal risk of injury or death, but my guess is you have already made peace with those facets of law enforcement. That said, military training can develop and strengthen poise, critical thinking, problem solving and attention to detail ....skills that can help you avoid similar incidences that have been exposed in the media which gave framework to the BLM movement and others in kind. I think you will be put in an equitable position to develop a more articulate level of judgement, enabling you to fare better than those who did not benefit from military training.

Other than that, if you do go the MP route, take it from me - Don't rub your eyes after getting blasted with capsacin! It's a total drag, man! Thanks in advance for your service.

Two kinds of regret. Regretting what you've done, and regretting what you haven't done.

It's your story to write...
So go and write it.

It all depends on what you see as best for you. I have many NCO in my reserve units that are cops and base security and with Infantry being our MOS it helps them but there really isn't a right or wrong answer here it's all what you think is best for you.