The US/Allies were fine with the March 1917 revolution--the Karenski government kept shooting American/Allied bullets with American/Allied guns against the Germans on the eastern front. The Allies weren't happy with the Bolsheviks making peace with the Germans and then taking those guns and bullets and fighting other Russians with them.

Edit: In fact, the American president was more than pleased that in his request for the US to declare war that, with the "democratic" Karenski government, the war had become Democracy vs Autocratic and it was ok to enter at that point on the side of Democracy.

The Tsar would have probably been a better choice looking in hindsight. Most likely would have resulted in an eventual democracy.

I think not getting involved is usually the better choice. In hindsight, perhaps we could have prevented the USSR, but that would've required foresight that we didn't have. These days, we seem to make things way worse when we get involved, so we should just not get involved most of the time (beyond restricting trade, that is).