grammar - How do I say "I am the best" ? の,は or が and 私 or 俺?

I'm making a shirt for a (rather egotistical) friend of mine and so am trying to do something with the slogan "I am the best" for fun. I need something with four characters only, and would like to ask the difference between

私の一番, 私が一番, 私は一番,

and which one would be the most appropriate in the context that he is saying it of himself. My grammar is not fantastic. I understand that が would entail a meaning like "I am the number one" versus は which would be "I am a number one" (correct me if I'm wrong). One of my friends has suggested

俺が一番, 俺様一番

Can someone explain to me how 俺 and 私 differ then? I'm quite confused. Also, this is for a boy, just in case anyone wonders.

Answer

As you correctly note, the が in this context adds focus to the noun phrase:

私が一番
'I am the best.' or 'The best one is me'

私は一番
'I am the best.'

[私]{わたくし} is very formal and polite, and is not usually used other than in business conversations, [私]{わたし} is neutral with politeness, 俺 is rough, and 俺様 is self-appraising. Any of them will work with は or が.

私の一番 does not make sense. 俺様一番 without the particle が really sounds like a funny phrase made up by a non-Japanese speaker, the kind that indeed is often seen printed on T-shirts or tatoos.