For a great beach location, Bodrum is the palce... it's a beachside town/resort and everything revolves around the beach. You can also catch the hidrofoil to Greece, it's only an hour. There are spa's and hotels from 5 stars to B/B's depending on your budget..During the day it has a beach feel to it, at night there are lots of resturants, clubs and coffee shops.

In Istanbul we stayed at Hotel Amira, it's within the walls of the old Instanbul and all major tourist attractions are within a 10 minutes walk, the Grand Bazaar a little longer, 15 tops.

Not sure if you interested in going inland to Cappadocia, if you are it's a magical place and well worth the trip, we stayed at Yunak Evleri (Urgup) (www.yunak.com), one of the original cave hotels, it goes back to the 5th century, it's now a 4 star hotel.If in Urgup, make sure you have a meal at Ziggy's Shoppe and Cafe, amazing desserts..
Hope this helps a little

We visited Turkey last summer and our three spots were Istanbul (5 days), Kas (7 days) and Cappadocia (2 days, Hot Air Balloon ride is a must). Istanbul and Cappodocia are safe bets and you can choose the beach town from a variety of options. We chose Kas especially because it was very sleepy and we enjoyed our week there very much. Then again we had two kids in tow who loved Kas (we rented a 2 br villa with a pool) but we also made it to two of Turkey's best beaches - Patara (1 hour) and Kaputas (25 mins). Kas also has the advantage of being home to Captain Ergun and his boat (Gulsah) - one of our best days was to hire the boat for the day to snorkel in the Mediterranean. From Kas we did a day trip to the Greek Island of Meis which is even sleepier than Kas but has a bigger and more impressive blue cave compared to its more well known counterpart in Capri.

Turkey is such a beautiful country with such helpful people that you will not go wrong with any of the recommendations.

Although the posters above gave good recommendations, they missed the fact that you will be visiting in April.

April is one of the wettest months in most parts of Turkey and can be rather cool. Enjoying Bodrum beaches are out of the question unless you can swim in about 64-66 F water.

Kas will be somewhat warmer with the sea possibly going up to 67-68 but it will be almost deserted.

The warmest areas will be possibly Antalya and Side. Antalya is a large city but it has some excellent resorts to the West at Beldibi, Goynuk, Kemer and to the East at Lara, Belek.
Antalya has good medical facilities.

Side is, I think lovely in the pre-season with small, simple hotels and terrific beaches. It is quite close to Manavgat town which has medical facilities and good street markets. It is also partially built on some terrific antique ruins.

In both of these cases, having a rental car will be very useful.

My recent trip report "From Denver to Virtuous" on Fodors mentions our one night stay in Side.

For Istanbul, I do not recommend Sultanahmet old town for foodies at all. The good food is at Nisantasi, Ulus, Etiler and along the Bosphorus. Sultanahmet has touristic food for the trade.

If not above your budget, you will love Bebek Hotel or Radisson Blu (sea view room) or House hotel at Ortakoy or Nisantasi. If you have points you can use the W and ParkSa Hilton are two other possibilities.

Istanbul should have the annual tulip festival going on.
The best hospital in Istanbul is the American Hospital at Nisantasi.
I recommend the upscale Changa, Muze de Changa, Ulus 29, Borsa Taksim, Deniz Ati restaurants, the simple Bursa Garaj, Tatbak, Oz Kilis middle of the road Husrev, Hunkar, Savoy Balik, Set Balik.

If you are staying on the Bosphorus or close to it, there is a small ferry which makes about five continuous trips between five piers on each of the European and Asian sides of the Bosphorus. Take that to enjoy a short cruise to reach the special yoghurt of Kanlica or the terrific fried horse mackerel at Sunanin Yeri at Kandilli on the Asian side.
schedules should be on: www.sehirhatlari.com at Istinye...Cengelkoy line.

Cappadocia will always be terrific.

Thank You All for your responses-
Otherchelebi- thanks for picking up on the weather dillema! Damn I had read that the avg weather there would be mid 80's... I"m super bummed- do you feel that in early April time on the beach will not be an option at all? It's kinda tricky for us since we can't go much later since I'll be too pregnant and I really want some beach time but also a different culture- I'm played out with Mexico. Thanks for your suggestions!