One rule of mine I'm sticking to:
at least to a point, smaller is more realistic, and is thus better.
A fictional country that's, say, over 1 million sq km in size and has over 50 million people will be harder to put into the real world than a country that's 1% of each (i.e. 10 000 sq km and 500 000 people)
This country has a unique name (kinda expected).
I don't want it to make people think of countries of a particular language, such as El Salvador (Spanish), Cape Verde (Portuguese), Austria (German), or New Zealand (English), with the attendant "I know [a notable world language] and such a country would stick out." Thus I created the name of a fictional language that they speak. It has fewer than 1 million speakers and is unlike other languages.
The country is not only independent, but almost thumbs its nose at big powers (perhaps if Trump gave its president a call, the latter might reply with a "Not now, I'm busy. I'll call you back when I have time.").
For this reason it probably spends disproportionately more on defense and maybe 10% of the male population is in the country's armed forces.
They are mostly a liberal democracy, and a republic, though can be socially conservative.
While the country can feed itself and has small industries, it's not resource rich, and became prosperous relatively recently— perhaps starting in the 1980s.
Getting back to the question: Should it be an island, landlocked, or be on the mainland with a coast?
It seems to me that island nations are more noticeable. Perhaps more English-speakers have heard of Jamaica than Burundi, even though the later has 2.5x the area, 5x the population (though, to be fair, a fraction of Jamaica's GDP).
Also it seems a lot of island nations tended to be former British colonies, and as such are probably beholden a bit to the United Kingdom, and its cousin, the US. If my character ran afoul with the US government (though he's not a terrorist), he might be extradited with relative ease.
If the country was landlocked and either in, or near, the interior of the continent, it could be bigger with less notice, but it would be beholden to the country that surrounds it.
The problem of being sealed off is that when it develops its tertiary sector, the big neighbours might hinder it. One can't have much of a tax haven, secret bank accounts, and/or mixed casinos and brothels where one can smoke marijuana legally, if the countries surrounding it restricts people from accessing the country, or block trade.
A compromise might be a mainline country with a coast, even if it accounted for a fraction of its border. It might have a corridor to the bulk of the country, though I'm not sure if the neighbours would have allowed such during its formation. I've also thought of air corridors, but aside of the wp:West Berlin Air Corridor, I know of no others, and I don't know how such a corridor could be maintained without big power help.
Suggestions and thoughts?
Thank you. 🙂