Great question! I am upvoting! Also just want to say that I am very sorry that Ukraine is left alone and as a Polish citizen (now living in London) I will try to help in whatever capacity I can. My friends are already helping in Poland with transport and housing for refugees. We stand with Ukraine! We are very sorry that the World is just standing and watching this, we hope there will be more sanctions and weapons delivered soon.
And yeah I join your problem - also not sure what are the best opportunities to donate to. So far I supported Polish Humanitarian Action, because they already were helping in Ukraine, so they know organizations on the ground, and they are respected and trustworthy (they helped in many war zones since 1992, including Syria, Iraq, Afghanistan or Chechnya). However, I would like to donate to a Ukrainian organization but it's hard for me to understand where is the best place to donate.
I will however support Ukrainian refugees directly. Either with money, transport, or housing in London if needed.
All the best to you! I hope your friends and family are safe!