I have voted for the Mediterranean region, for several different reasons.

First of let me tell you that beeing in the business for some time now, I have had the chance to take a professional look to almost everywhere from Çeşme to Alanya, and with all my respect to other professionals working in the Turkish market here are some thoughts.

1 - The Mediterranean region has a better international infrastructure
For those who may not be aware of it, the Mediterranean region of Turkey is the "touristic capital" of Turkey. Antalya international airport is the second most busiest Airport of Turkey (after Istanbul), with flights from and to all major E.U countries all year long. On the other hand, with a governmental initiative to expand touristic income (which started in mid 80's) the Mediterranean coast of Turkey, starting with Antalya,was chosen as the primary region to develop, and in an array of 20 years hundreds of big/medium/small hotels were build, attracting millions of tourists a year.
To sum up, thanks to a state initiative, the Mediterranean region acquired a serious international know-how.

2 - Golf
Belek is now considered as the golf capital of Turkey, and although a little late, the Aegean region is also trying to catch up with this lack they have. Its good for sure for the entire business, but for places such as Bodrum or Altinkum to professionalize as much as the Mediterranean will take some time

3 - New Investments
With the announcement of the opening of a new international airport in Gazipasa (30 km south to Alanya), the region has welcomed a major infrastructural tool needed so badly for a long time.
Alanya, for now at an hour from the nearest international airport (Antalya), was generating until now 7% of total tourism income (+/- 1 billion $), and this new airport will only help to improve this to higher levels.
To that we should also add new investments such as golf courses, 5 star international hotels etc.

4 - Better price/quality ratio
When investing in a property, no matter if its overseas or not, I think that the goal should be to get the better price/quality ratio possible, which basically is pretty easily achievable in the Mediterranean coast.

Dont get me wrong, by that I absolutely dont want to mean that the Aegean coast of Turkey is worthless, not at all. Each region has its own beauty, advantages, points of appeal etc...