Politics Magazine
These charts represent the results of the newest Economist / YouGov Poll -- done between April 27th and 30th of 597 nationwide Democrats and Independents who will vote in a Democratic primary/caucus. No margin of error was given for this group, but it was likely in the area of about 4 points.
The poll asked voters who they are considering supporting in the primary, and allowed them to choose as many candidates as they are actually considering. The second chart is most interesting. It shows that most voters are considering between 1 and 8 candidates, with the biggest group (33%) considering between 2 and 4 candidates.
I think this is accurate. Most Democrats (and Democratic leaners) have not made a solid choice yet. They are waiting for a candidate to impress them, and likely will not make up their minds until the June debates -- maybe even later.