Which one is best keyshot or solidworks visualize?

This depends on what you're intending to do/model on these programs.

Regarding graphics/visual quality, in general Keyshot is a better program than Solidworks PV360 (Photo View) or Solidworks Visualize. Solidworks tends to focus on a more industrial side to things. Its PV360 and Visualize programs are designed for providing quick concept images (PV360 in particular). Visualize however is a much more advanced version which can provide highly detailed models on Par with Keyshot. Keyshot tends to focus highly on it's photorealistic capabilities, having a highly complex materials system which leads to accurately represented complex finishes/materials. Keyshot also has flexible import systems/plugins which can allow you to easily import Solidworks files into its program.

That being said, both Visualize and Keyshot will perform on par with each other and will both create highly realistic images (Keyshot may do this faster). It really comes down to how the model is made that will effect its rendering.

Based on your product.if you are doing render for visualizing purpose only SW is enough.you want to more realistic go to Keyshot. But sometimes SW rendering looks like keyshot.i seen some legends model in grabcad and real time those are using SW only that models are looking cool.you are beginner SW is enough.

My opinion for your question is 1) our interest 2) the way we are using SW rendering.

"Which one is best" is really not a great question to ask.
Best at what?

With such limited information to go on, I can only suggest trying both programs and deciding which will work "best" for you.

Simply Keyshot is

Keyshoot is the best....