I've owned both an Amazon and an 1800, and I've worked on a whole bunch of others. The 1800 is not heavier (except for the ES) -- the coupes weigh just about the same as the Amazon sedans. The space under the hood is exactly the same. Maintenance and routine repairs are not any more difficult on either car. The rear seat of the 1800 is useless for carrying passengers (including the ES), but it folds down and you can fit a whole lot of cargo in there.

The 1800's ergonomics take some getting used to. It's harder to get in and out of than an Amazon, the window winders are too far back, and you work the heater controls by feel. OTOH, there's almost no wind noise in an 1800 -- it's the only car I know of where you can roll both windows all the way down and carry on a conversation in normal tones on the freeway. The seats are very different, but equally comfortable on both cars (extremely comfortable when in good shape).

PVs are fun and funky, but not what I'd want to take a coast-to-coast trip in unless I had a lot of time and was going by back roads. Working under the dash is near impossible, you have to keep up with all the grease fittings, and I have safety concerns in several areas (for one, the steering column is a spear pointed at your heart in a frontal crash).

I like the first few years of the 140 a lot -- I have a friend who says, "Volvo took the Amazon and polished it until it glows." They are noticeably heavier, and I find them harder to work on. It's a long reach to stuff under the hood, and you can't even see the idle speed screw on the rear carb. The heater core is in the dash where it's a pain to get to -- it's a lot of little things like that I find annoying. They do have tons of room and they are the safest of the lot.