the largest I've ever run was Blueline Airways in S4B. it had 12 hubs (more realistic as American Airlines' got 10) flying to over 350 destinations worldwide (AA also operates to over 350 destinations) with a fleet of 905 aircraft + 100+ orders at the world's reset. (AA's got like 900 so mines very realistic) shame I was in 11th place on valuation (couple of spamliners) and 12th in valuation.
Well, you didn't lose much as the sandbox worlds have no awards...