It's actually a very simplistic and naïve answer. One should look carefully at the business model of the carrier; their future growth plans; their current pilot list; current upgrade time; projected attrition; projected upgrade time for someone hired today based on the growth plans and attrition; rosters; quality of life; benefits; cost of living; long term career growth potential; culture of the host country; flight deck culture of the specific carrier; and a whole host of other factors.
Typhoonpilot