The region is changing so quickly that it is impossible to predict the situation in 3 years' time.
Many candidates face the issue that the company they work for has a much better reputation back home than is the case here. Also it is often the case that a company does not offer the full portfolio of services over here. E&Y and CGEY are basically auditors with small consulting practices. CGEY has a slightly better reputation than E&Y but neither are market leaders in consulting (technical or otherwise) out here. BT would be the one to go for out of the 3 (although none really lend themselves to your objective perfectly), as an incumbent operator from a country held in strong esteem will carry some weight. BT operates here more as a consulting/system integration/service provider organisation and is reasonably well viewed in comparison to the other 2. Tradition and history count for a lot and BT used to own large stakes in some of the telco companies out here.
3 years is plenty of time for any of these companies to change their position in the market significantly so you are second guessing really and my advice would be to go for the best job now and not worry too much about what you will be doing in 3 years time. Cost of living is rising so quickly here that it might be prohibitively expensive to make the move by then anyway.
Hopefully in 3 years time, either the currency will no longer be pegged to the dollar or the dollar will have bouced back.
.... planning 3 years ahead .... very impressive. I don't know what I am doing next week!!