98obl-CMH

I have spent the better part of the last hour reading posts and learning about the head gasket leak that plague 2.5l engines, as well as far more about how car engines work than I ever dreamed. My '98 Outback Limited wagon has 80k on it and has been a dream car until 3-4 weeks ago when the overheating began, leaking coolant, white smoke out of the exhaust, etc. My mechanic suggests the engine be replaced and mentioned he would look into a used one when I dropped the car off today (The car has been to the dealership many times, as well.) His suggestion made me worry that we would simply be buying an engine that would eventually exhibit the same problem. A few comments in various replies here on USMB give me the impression that this is a possibility. I welcome your suggestions on how to proceed assuming the engine will be replaced. Should the 2.5l be avoided altogether, new, used, or rebuilt? Should a 2.2 be used instead? If so, are there drawbacks? Thanks so much for any words of wisdom. I am at my wits end on this one.