The best outcome for the Democrats, and for the country as a whole, would be for Crist to pull a full-Lieberman and run as an "Independent Republican." That would have tremendous "debranding" value, since it would help prove to the country that sane people do not have a place in the Republican party.
Crist, of course, would not do that, since it would debilitate him among moderate and conservative white Democrats, whom he would need to peel away from Meek in order to have a shot. As he tries to do this, however, he will permit Rubio to say that he's the only conservative in the race. If Rubio can hold 80-90% of Republicans and get enough independents, he'll still be in the driver's seat, since the Democratic vote will split more than the Republican vote and, sadly, along racial lines.
More importantly, as a full independent without affiliation, Crist would have better access to the lower turnout white independents who would decide the race. I don't see Meek getting too much of that vote, whereas I could see Rubio making a cynical, successful play at it against a decreasingly popular incumbent white governor.