Thanks for all your input!

There is a physical crack in the heat exchanger and all 3 people that I spoke with said that I cannot turn on the furnace for any reason if I want to wake up in the morning. The first guy that came for a routine inspection and found the cracks posted a note on the machine that we are not allowed to turn it on by law. The furnace is 17 years old.

All three companies seem very reliable and two have been in business over 20 years so I think they would all do a good job. I think I'll take the Trane off the list since it was the priciest and per TrapperL its no more reliable than the Ruud.

The Lennox and Ruud models are both 5 tons, high efficiency (95%) two stage, variable speed motor. The a/cs are both high efficiency too. The Ruud package is about $1000 more than the Lennox. Also, the Ruud was quoted with less money back in rebates & tax credits.

Right now I'm leaning towards the Lennox since it's less and I can't tell what the difference really is between the 2. But, MrRational is installing a Ruud and how can you argue with a name like that?