Griffin and I did a blind tasting of O'Fallon, Dogfish Punk, and New Holland Icabod last year. Now, it is true that each year is a little different, but in general O'Fallon has been a winner each of the last two years.
Last year, we both preferred O'Fallon, then Ichabod. Dogfish Punk was notably inferior to the other two (despite Griffin having liked the 2005 version the best).
O'Fallon is a pumpkin beer that actually captures the fruity essence of pumpkin (not the spices -- which have given pumpkin beers a bad image to many).
The OF aroma has some clove and nutmeg, but these are not overwhelming.
The taste has the pleasing sweetness of fruit. There was a little spicing, but it was moderate and not overwhelming. There was also a hefeweizen quality about it, some interesting yeast things going on.
I would not have known the Ichabod was a pumpkin beer if I were not told. Perhaps because the Pumpkin flavor was so pronounced in the O"Fallon, the Ichabod was neither pie-spiced or overly pumkinny. Instead it was an interesting seasonal ale with some hops and a nice malt profile.
The Punk was the orangest of the beers in color, and as opposed to previous years, the really went full on with the allspice. Perhaps they have changed back this year, but the spicing was too assertive in 2006.
Another Pumpkin beer that we did try this year, was the Southern Tier Pumking which we also liked. I can't find my tasting notes, but it was a darker beer than most, with some bready qualities. The spicing complemented the pumpkin and the sugars/high ABV made this a strong contender. You can only get bombers of this one, so it would be a tasting beer to have in addition to the stuff you'd put out for people to grab from a cooler.
We haven't tried Post Road, but it is a spin off brand of Brooklyn Brewery (which has an excellent brewer, Garrett Oliver, also known in food circles).
I have heard the Post Road is similar in profile to the O'Fallon (you get the pumpkin and not a mouth full of spice).
Lakefront is well known for its assertive spicing. So if you ARE looking for an option with (imho VERY) evident spice, then that is a good choice for you.
All this said, I think that for your purposes, a selection of Oktoberfests (with maybe only a few pumpkin beers) might be an easier crossover for the BMC regulars while they are still in the spirit of the seasonal theme.
Prost!