Well, the 83 flathood is fantastic. All the advantages of the basic 240 (safety, amazing handling, and good square looks) with a touch of the exotic in the front end as well as the amazing power of the B21FTIC. And all parts are available in pick and pulls for $0.05 on the dealer dollar, if you like the hunting for them. But a turbo replacement is a hit, when needed.
The 1800 is a real cool car made out of heavy duty parts. It is hard not to admire the way they were built. The parts sell on Ebay for relatively high prices so it is not the low rent thing the 240 is. I would buy a car someone else restored unless you are a masochist. The 122 is pretty cool too, but last time I went to look at one, I drove the 780 and the 122 looked anemic when compared to that car, considering the roughly equal values. I hear a lot of 122 parts are still available from Napa. They do drive very nicely with a lot of solid 240 feel to them.
Obviously, I am not an 1800 (other than the one I am parting out) or 122 expert or owner but they do tempt me. Driving an 1800 feels like wearing a diving helmet because the visibility is so poor compared to the later Volvos.