Post 1956 Johnson or Evinrude is your best bet.
Would you insist on listening to a used outboard before buying it?
If I didn't want a project (I have bought about 10 motors in the past 3 years, and none of them were in running condition when bought), I would definitely insist on hearing it run. Plus, I would do a compression check, and inspect the gear lube.
I put post 1956, as they are the best as far as reliability, and ease to get parts for, etc, but you probably want something a little more modern for ease of use. I would put that around post 1970 or so Johnson/Evinrude, as they had pretty well modernized them to the point that they would be until about when the 4 strokes came out by that point. Post 1985 is going to be propshaft rated, as opposed to crankshaft rated, so there will be a 10% difference in hp between the two years, but that is not going to be a deal breaker. The mid 70s is when we started seeing electronic ignition, over points, but they are both simple, reliable and easy to work on, so it doesn't matter there. Really, in the small Johnnyrude twin cylinders, you can't go wrong after '70 or so. Just look at condition.
Other brands are possibilities too. If you go a little newer, you can find some smaller Yamahas as well. Their small 2 stroke motors are pretty good as well.
I can't vouch too much for them, but the older 2 stroke Tohatsu's seem to be good motors as well. I almost powered my Yazoo with one.
Hondas will cost you a bloody fortune, but they are excellent motors, as anything of Honda's is. However, they weren't as common back in the '70s and '80s as some of the other brands, so I would be leary of parts availability for them.
Stay away from Chrysler or Force at all costs. Even if it is one of the Mercury made Force's, it was still the Chrysler design, just Merc was getting the meager profits from them.
I am not a Merc person at all. Their older ones were crazy, to say the least. Great racing motors, but really had no place on a boat that needed to be reliable. The new ones, well, I am not going to go there. However, it is a very wide common speculation that the only reason that both merc and Motorguide are still in business is due to the number of boat companies that Brunswick owns, and packages merc/motorguide combos on. That leaves a small window, mostly in the '90s, of the reasonable motors, IMHO, but I just prefer to stay away from them altogether.
So, I would highly recommend a Johnson/Evinrude. Partly because that is what I am most familiar, but there is a reason that I choose them as my main interest in motors. They usually have the most logical/bulletproof designs, that lasted longer than other motors before being changed to a new model. They (especially the twin cyl. motors) are known as the industry standard for a long lasting reliable motor. Probably the easiest motor to get parts for, and simplest motor to work on.
Don't be afraid of motors with some age. My main motor is a '75 Evinrude 40 horse tiller. It gets quite a bit of use just about every weekend. Very reliable, and I have no issues taking it out in the ocean, or fishing bass tourneys with it, or putting in, and running downriver, as I know it will get me back up.
