A common situation vs. an unknown

[AZplaya]

I think most decent players are able to figure out the best line to take when they have a read/stats/both on a Villian. I personally find the most difficult decisions to be against an unknown player. There are many on this forum who advocate assuming an unknown is a donk until proven otherwise. Still equally as many prefer to wait until a read is established before making assumptions about an opponents play. The purpose of this post is to look at the pro's and con's of each school of thought. I hope to generate discussion from posters as to whether it's best to assume our opponents are fish or to wait for a specific read. I present the following scenario to generate this discussion. For this hand assume full stacks.

Hero has just sat down at a Party NL$100 6max table. Hero waits for BB, post, and is kindly dealt A [img]/images/graemlins/diamond.gif[/img]A [img]/images/graemlins/spade.gif[/img] for his first hand. Folded around to CO who covers, CO raises to $4. Unfortunatley hero has no stats, notes, or reads on this opponent. Folded to Hero, Hero makes it $15, CO calls. Pot is now ~$30. Flop comes down: Q [img]/images/graemlins/diamond.gif[/img]J [img]/images/graemlins/heart.gif[/img]6 [img]/images/graemlins/spade.gif[/img], Hero leads for $25, CO raises to $75, Hero???

Push or fold, and why?