When we went there the best was some travellers cheques in sterling and a wedge of euros. The locals turned their noses up at Turkish currency but euros were no problem.
Travellers cheques are fine but be wary where you cash them. Try to use a bank or reputable hotel. DON'T go near the booths they have in some resorts as they often rip off tourists and if you've already signed the cheques you probably won't be able to use them elsewhere. enjoy your holiday.