What do you think of this argument for God?

[Nonpareil]

That is the major fallacy of all variations of the ontological argument. They assume God is logically necessary and go from there.

Well, not exactly. They try to assert that God is logically necessary by defining the term "God" as "a being that is logically necessary".

Unfortunately, even if we were to grant that the definition is coherent - and it usually isn't - merely defining something as necessary does not establish that there exists an actual instance of that object. You still have to show that there is an actual logical necessity. I can define unicorns as logically necessary, but that doesn't mean that they actually are.

It's just bare assertion which quickly becomes circular logic, because theistic philosophers, as a rule, are very bad at their jobs.