As a glider pilot, I think a lot about landing in fields, and do it moderately routinely.
As has been commented, the answer to "where to go" depends dramatically on the aircraft that you're in.
A cornfield is a almost-guaranteed crash for a fixed undercarriage nose-wheel aircraft. But it's probably a nice soft bed for a jumbo.
If we limit ourselves to aircraft with less than two engines, the main factors that come into play are:
- Retractable under carriage
- Nose wheel or tail dragger
- High or low wing configuration
Retractable undercarriage affects your choice of outlanding, because it gives you the opportunity to take the wheels away from a grabby crop (or water).
Nose wheel or tail dragger affects your choice because it affects which part of the aircraft will hit the grabby crop first, and affects the centre of gravity of the configration at the time this happens. You want tail-first low CofG in a grabby crop.
High or low wing configuration affects the choice because a low wing configuration means that the posts on the side of a single lane road are significant, and a crop can grab them.
The "types" of outlanding choices that you have fall into categories that include:
- Empty fallow field
- Stocked field (and whether the stock is spread out or in one corner)
- Recently harvested wheat - low
- Recently harvested wheat - high
Each of these (and choices similar) have different characteristics, and the choice "chart" for each is different depending on the aircraft configuration variables mentioned above.
It may surprise you that corn and canola are grouped together, given that corn has massive cobs, and canola does not. But actually the major factor for this type of crop is it's depth and "grabby-ness". Canola is only marginally better to land in than corn, because it is not as deep. But is is just as grabby.
This is why corn/canola is a certified crash for a nose-wheel fixed undercarriage aircraft. Unless you are a gun pilot with a cunning plan to get around it - in which case your approach will be anything but normal - that crop is going to grab your mainwheels and you're going in nose first: bang.
In a taildragger, you have the opportunity to come in nose-high and have the tail-wheel grab first. In this instance, depending on the stall-speed of your aircraft (IE how fast you are going when this happens) it might turn into a "landing" instead of a "crash".
But if you have low wings, then you're still in trouble, because the chances are quite reasonable that this grabby crop will grab a wingtip, and boom - crash.
On a road, if you have high wings, then you are in good shape.
You asked "should a road ever be considered?". ONLY IF there is NO traffic. In a small aircraft, with less than a handful of passengers, you have no right to risk the life of people travelling on a road, which is what you will be doing if you put down on it while they are driving on it. If you suprise just a single car doing country road speeds, that driver can end up rolled in a ditch.
So ONLY if I had a high wing aicraft with a deserted straight road would I consider that - and then it is actually quite attractive.
(Edit: in case it isn't obvious, vines are death).