Hard to operate in China or Russia? lol, wut?
What's wrong with Ukraine that there are so many posts about it? I don't see how would it be harder then in smaller non-EU neighbors like Belarus or Georgia.
So I would make two big divisions:
Hardest to have decent growth:
- smaller or more troubled African countries (i.e. about more than half of continent), what kind of passenger load could you expect from Eritrea, Gambia, Swaziland, Central African Republic, or Somalia? A lot of neighboring countries and airports but all with same problems and small loads, you can barely fill a few 737s at best.
- anything in the Pacific, not only small load but also distance
- small countries surrounded by big competitive neighbors in Asia, Europe and the Caribbean (like Laos, Bhutan, Montenegro, Grenada)
Hardest competition (dependent on other players in a particular world):
all big markets, but usually 1/10 of all airlines are in USA so that says enough, but sometimes you'll also get a lot of competition in EU (especially big members like Germany, UK, France, Spain), Japan, China, Russia, Australia, Turkey, sometimes Brazil, India, Indonesia, also in Singapore or Persian Gulf when sometimes you have 5 airlines who all want to connect every town on Earth with their hub; but there are a lot of opportunities and it basically depends on your abilities and time, and sometimes you can get more or less lucky about how numerous, capable and/or stubborn your domestic opponents will be.