I often bought the most expensive ship, in the cheapest category (think it was $5m or so) in the beginning.
Chose New York as home, hoped for an offer to sail with arms to Dar-Es-Saleem (I believe the name was, in the Middle-East). Cost $10.000 to pass the Suez, but otherwise risk-free.
Always buy the best ship within your range, when the price of ships are low. Don't spend time on cheap ones.
