Can digital servos be used with the Optima receiver?

Do you mean the receiver sold by Hitec called the Optima or something else? If it's the Hitec one, the answer is yes.

Hello!

I am thinking to buy a new digital servo and I am wonder about the differences between the servo motors for example: brushed, brushless and coreless servo...which is the fastest, the most percise, which has most powerfull torque and which work at the lowest energy level. Into consideration am am looking for metal gear, double ball bearing, standard size servo motor with 25T and JR plug for steering aplication on 1/10 scale onroad chassis. If I am correct any of the mentioned type of servo motors will work on each transmitter and receiver I need to look only that I have a JR plug on both sides? Any ideas which servo motor should I buy? Price limitation around 35 EUR or 40$.

Thanks.

In that price range you can get, at best, a Savox servo with metal gears or one of the Chinese un-brand ones of dubious specs. Brushless, etc. are questions to worry about if moving up about twice in price but that being said, a good servo is something you buy once, a cheaper servo is something you'll probably replace with something more expensive later on anyway.