GIVE ANSWERS - Limba Română

I'm starting to learn Romanian and my only means to ask is to ask in English, which is more international than my Spanish. I have a question in which I don't know which of these Romanian "good morning" is the correct form. Here is a complete list of what I found and you tell me which is the most "proper" one. I know not everyone pronounces their "good morning" the same, depending of the county and region, but mostly I want to know which one would be gramatically more correct to use if you wanted to publish a formal paper for example.

1. Bună dimineaţa

2. Bună dimineața

3. Buna dimineata

4. Bunã dimineață

Thank you in advance for your help. Sorry if I'm not writing this in Romanian. I'm still learning the ropes :(