infinitive or present continuous?

Well, both make sense.

To get there - and stay there - you will need to be creative as well as efficient, and constantly proving yourself.

In the sentence above you say that someone needs to be proving themselves. The structure is be + adjective + adjective + present participle. In other words, be creative, be efficient, and be proving yourself (it's the Present Continuous form).

To get there - and stay there - you will need to be creative as well as efficient, and constantly prove yourself.

In the sentence above, using 2 verbs, you say not what the person should be like, but what they should do: be creative and efficient, and prove yourself. So, this person needs to do 2 things, and have 2 qualities - creativity and efficiency.

Personally, I'd use the second sentence.