As I have explained in other posts, I am neither for nor against a Rainbow or a Red-Green deal, the deal that I want is the one that is best for Wales and the one that is best for Plaid.
My own political prejudices lead me to favour the Rainbow, because my own political views, if I lived in England, would lead me to support the Conservatives rather than Labour in an election (unless there was an English Democrat standing, of course).
Which ever side Plaid chooses to back, the losing side will accuse it of opportunism and selling its soul to the devil. The vitriol that comes from the losing side will make Sanddef's stirred in a bucket variety unworthy of third prize in the village show, even if Adam Price is the adjudicator for the jam, vitriol and chutney category. So the slagging that Plaid might get from the other parties as a result of its choice is immaterial.
Clearly, given the choice, from a purely Plaid point of view a Plaid First Minister is better for Plaid than a First Minister from any other party.
The other party political issue, and by far the most important, is that an alliance with, what many see, as the evil which is Tory, will be damaging to Plaid's future electoral chances. However the negotiators must remember that many people voted Plaid as an alternative to Labour, if Plaid delivers another Labour Government then they might see this as a kick in the teeth.
On the other hand there is a deep seated hatred of the Conservative party amongst some sections of the Welsh population, which in some areas is still as much to do with the evictions of 1859 as it is to do with the Thatcher Government of 1979. An anti Tory prejudice that would be illegal under discrimination laws if it pertained to any other issue other than party politics.
But a prejudice that, as the Rainbow Rebels quite rightly pointed out, Plaid can not afford to ignore. However Plaid has probably already peed on its chips in this respect by entertaining the possibility of a Tory including coalition for the past month or so. Plaid has shown its willingness to sup with the Tory devil, and even if it jibs at buying its round at last orders, the damage has been done and can only be undone by showing that Green + Blue = success.
From a party interest prospective the Rainbow is best for Plaid by a long shot.