I had an '85 Buick Lesabre years ago with an olds 307 engine. It was pretty underpowered... but did the job. Got about 19-20mpg on the highway. Plenty reliable- though the spaghetti-bowl vacuum circuits and AIR system required occasional tinkering. Probably would've been a pain to work on except that I never really had to do much to the engine.
I bought the car in 1996, with 120,000 miles- the transmission had just been rebuilt. I crashed it a few years later with 185,000 miles. Pulled the engine and tranny... put them in an '84 Grand Prix... drove it another 20k before I traded it off. The engine never used a bit of oil- though it was a little crusty with minor leaks. Got about 22mpg in that Grand Prix- but that was with the 2004R overdrive tranny and a ridiculous 2.29:1 rear axle ratio.
I traded that Grand Prix in on an '85 Caprice with a 305. It had more power on takeoff, but didn't seem to do as well at highway speeds (had to downshift more on the hills). Got about 1mpg better than the 307. Maybe 20 or 21 on the highway. Never used oil. Required a little more tinkering to keep it runnning right (again with the vacuum system, carburator adjustment, etc.).
Neither was anything spectacular, but they'd move the car down the road at highway speed- and that's all I really need. Given the choice between the two, I probably have a very SLIGHT preference for the 307. That Buick was really nice on the highway- a great car for road trips. The Caprice did ok, but for whatever reason, the 305 just didn't have as much power at 75mph as the 307. And I don't care a whole lot about acceleration from a dead stop (where the 305 was clearly better).