What’s the best vitamin to buy for men?

You're best to find out, through testing, what you're deficient in and supplement appropriately. And to also look at your diet and address why you're not getting sufficient nutrition.

We can come at least close to getting most micronutrients from our food with a bit of attention to it. I do. (In MFP, if you want to track micros, it's important to vet the database entries you choose for micronutrient accuracy.)

Food - to the extent possible - is the best option. Averaging pretty close to reasonable goals will be fine: You don't need to be exactly exact every single day.

Then, as others suggest, get tested after eating in a well rounded way for a while, see if you're low on anything. (Some test results can be distorted by supplementing before testing.)

This is a thing you can safely take a bit of time to work out, as long as not already diagnosed with a deficiency or relevant health condition. Most supplements are overkill, and just create expensive urine. Overdoing some of the fat-soluble vitamins (A, D, E, K) via supplements can even be risky.

As someone who worked at a major research university, I knew some nutrition researchers (even though, to be clear, I'm not a credentialed expert myself). Those people didn't take supplements, just focused on a healthy diet. They said it was OK to take some moderate-dose mainstream multivitamin as a bit of insurance, though not necessary, but didn't recommend doing anything more complicated with supplements unless medically directed.

YMMV.

My view is that I wouldn't take any supplements unless a proven deficiency or specific medical reason.