[LearnAmazingJapanese]

My two sense...er cents:

"This is the best"

...translates a bit differently depending on context:

This is the best (I've ever eaten, etc.)...

Kore ga saikou desu

This is the best (decision, etc..)...

Kore ga ichiban ii desu

or

Kono hou ga ii desu (this is "better" or "the best" option)

And so forth.

If there was a little more context available, we could probably get you the most appropriate translation for the situation.

Sore ja.