It's early in the season yet for these businesses to reply to emails, leave it till nearer your holiday. We usually book about 2 weeks before we leave.
I would also always recommend using a local company that is near where you are staying. Booking a car from Dalaman and then having problems with it, will mean waiting until someone comes from Dalaman. Book it locally and someone will be with you much quicker.
We have always used Fethiye Lovers (for about 5 years now). The are nice and handy in Calis and have newish cars, no old banger with little power, which we have experienced in the past. Remember cheapest may not always be the best.