I am not keen on Lennox equipment. They have improved their quality in the last few years but I still remember them as "not reliable". That is probably the cause of your premature breakdown.
In my mind the only difference between Janitrol and Lennox is the dollars. Though as I said Lennox has improved dramatically.
The big question here is....Do you plan on staying in this house for many years? Do the weather patterns where you live make a/c a must? Will replacing this unit cause you major financial duress?
If you can afford it, I would replace condensor with a like unit. I probably would upgrade to a 3 ton but if it cooled your house in the past, maybe just stay with the 2.5 ton unit. Without a doubt use a 12 seer unit. If you wont be staying there for very long and money is a problem then go Janitrol.
I have sold many Janitrol units and their reliability has been no worse than any other unit. They are built by one of the biggest companies in the business and they would not still be around if they were junk. The "fit and finish" of these units aren't as good as the others, I think that is where they saved on production costs. Janitrol condensors aren't the quietest on the market, but I have seen many Carriers that are louder. Poor installation has caused most of the problems. Their warrranties are as good as anyone elses. In fact they are the company that caused everyone else to extend their warranties to keep pace. If you want quiet get a unit with the scroll compressor.
If this was my house.....I would replace the condensor with a 12 seer Lennox unit from a reputable Lennox dealer. Though you could use any brand with it. If money was a real important factor then I would go the Janitrol route.