As mentioned above, all the different brands of ac/furnaces generally use the same parts inside, with slight differences. Lennox makes high quality stuff, but they use more proprietary parts than other brands and are on the higher side of pricing. Generally, any unit should give you at least 10 years of service with little problems if its installed correctly. The installer is far more important than the brand of unit with hvac. Since you have a leak in your system, make sure they run new lineset. That may require cutting some drywall because your furnaces are located in your attic