I planted several different varieties last year and they all produced poorly. Could of been the weather though....lots of lots of rain....
Last year was pretty rough tomato growing weather. My hybrids didn't do well either, so I think much of it was weather. Having said that, IMO heirlooms don't have near the disease resistance to make it half a season here. My dad is dead set on planting heirlooms this year. I told him we would have to plant tomatoes every month to have a crop all the way until fall.
Mike, the only heirloom I've ever tried is a pink German. They are good tomatoes and have potato shaped leaves. They grow large fruit and the green tomatoes off them will keep well into winter if you pull them right before the first frost.