Can someone give me advice what is best transport to use in Turkey?

I am planning to go there for about 14 days and I like to see as much as possible. It will be first time for me to go there. Probably it would be most easier for me to start in Istanbul.

Usually when I can I rent a car and drive around because of freedom feeling and most efficiently use of time. Cause sometimes waiting for public transport can take quite a lot of time and you have to take luggage all the time around places.

Of course Istanbul I will not use the car in Istanbul more than just necessary to leave the city. How crowded are road around the country and in what condition are? I like to see most interesting sites for my first trip and I prefer nature and some historic sites but also I like to taste some beaches.