Every new series Ford built was an upgrade from the one prior to it. The 3 cylinder tractors were a huge leap forward from the older 4 cyl models.
Not for what they can do (hp vs hp) but in terms of longevity and reliability they are. I happen to think they are easier to work on too though that may partly be because I'm more familiar with them. A 3 cyl model will still be very familiar to someone who's owned a 4 cylinder model.
I also ran gassers for a long time before I got my first diesel. I, like you, got tired of dinking around with points, spark, carbs and bad gas. I have a couple of diesels now and they always start and run. You can let one sit for a couple of years, go put a battery in it and it will start right up and go to work.
The worst drawbacks to a 3 cyl diesel is they stink - the fuel stinks and the exhaust especially stinks - and they are much more noisy compared to a gas engine.
A gasser is a lot more pleasant to be around.
If you can live with those two things they are the way to go.
The models you list are all good machines.
You'll more likely find one equipped with the best options the newer they are - PS, 8 speed, live PTO, differential lock, etc.
Don't buy one with the plain Jane 4 speed. 4 speed is okay but the 6 or 8 speeds are So much better
Remember this about the 3 cylinder Fords:
The 1965-75 Thousand Series had notoriously Bad tachs and hour meters. They quit early and often.
So NEVER trust the hours on one.
The later 26/36/4600 tractors, though they are nearly identical to the Thousands had better tachs and those tachs can usually be trusted.
When you go to look at a diesel, insist that it be stone cold when you get there. You don't want one that needs ether to get rolling in the morning and the seller has it "warmed up and ready for you" when you get there. Feel the temperature of the block when you get there to verify. A diesel will smoke a bit till it gets heated up but you don't want a cloud of blue smoke coming from one. Deisels do smoke more than a gasser will but run one for 10 minutes or more when you test drive it. The smoke should all-mosst clear up.
I live in cold country but never need to start mine spur of the moment. In December or January if we get a big snowfall so I need to clear the driveway I just plug the block heater in for an hour or so and it starts like it's July.
If you go look at one take a bunch of photos of it and post them here. We'll pick it apart and look it over for you. If you don't know how to post photos you can email them to me and I'll post them for you.
Here's a photo of my little brother on my 3000 diesel discing a newly turned deer plot last Saturday.
I wouldn't part with this tractor for anything.