Moving from Rakuten mobile to another carrier. Recommendation request

Hello.
I have been using Rakuten Mobile for several years already. Usually it doesn't work underground, but it was not an issue for me until my workplace moved to a new office.

I can't use the phone in my office because of the poor signal. I can at least get a weak signal if I stand by the window, but it is far from ideal.

My colleagues told me that Docomo and SoftBank work better here in this office. Any recommendations? Did someone try both in the past?

Edit: leaning towards Docomo because of the international roaming included in the package.