Boarding times at airports have doubled since the 1970s

Most Annoying Airline Delays Might Just Be in the Boarding by Jad Mouawad (NYT)

Boarding times at airports have doubled since the 1970s, prompting airlines to try all kinds of elaborate tricks to get passengers in speedily and leave the gate on time. Here is the link for the full article.
http://www.nytimes.com/2011/11/01/business/airlines-are-trying-to-cut-boarding-times-on-planes.html

So what is the best way to do this? Start from the last row, in sectors/zones like many airlines does or the first window and then aisle seats? Ryanair has the quickest turn-around time in the aviation industry as they board passengers from the rear door while off-loading the previous flight passengers from the front door or v.v. as they don't have any pre-assigned seats.

At SunExpress, we were using the zone system and inviting the rear seats first, then mid, and finally the front. However, if you are in an airport with poor facilities, your passengers had squeezed in the waiting lounge, or there is a delay, asking passengers to follow those instructions is very hard.

Here is a multimedia file from NYT to give you an idea about; Comparing Airplane Boarding Methods

For legacy airlines, I think block boarding is the best solution. I don't know which ones you have already experienced, but at least now you know the reason for almost full overhead bins in your flight ;)