I haven't seen comments from every Democrat, obviously, but most of what I've seen has parsed the issue in a pretty coherent way. It's not hypocritical to have been troubled by Comey's election adventures and to think that firing him now stinks to high heaven.
Another small detail that's interesting to note is that Rosenstein's letter, though highly critical of Comey, doesn't explicitly state that he should be removed. It's an obvious fig-leaf for a decision that came from the Oval Office.
Whatever hypocrisy exists on the D side here pales in comparison, IMO, to the cynicism and hypocrisy of taking the line that he was fired for the reasons set out in Rosenstein's letter, which were actions that were explicitly praised by the President. So, take note of Congressional hypocrisy, sure, but to make that the story here is to miss the point.
The President just fired the government official--in an office which is supposed to be firewalled from political considerations--who is overseeing an investigation of the President's campaign and former members of the Administration. This comes barely a month after that official publicly confirmed that the investigation existed, and declined to backstop the President's irresponsible wiretapping claims. This is not a "on one hand..." kind of issue.