If i got into a street fight which would be a better art to defend my self an internal(mainly Hsing I) or external art.
That depends. Who would be doing the fighting? You, or somebody else? My point is that it is both the art AND the artist that make the difference, and I tend to think it leans a bit more toward the artist, given the underestimated importance of psychological factors. Perhaps if you could give a bit more information on what you are choosing between, we could be of more help to you.
Im choosing mainly between Hsing I and praying mantis
Both can be very effective styles. The only thing I can offer is that there is a saying that “the Mantis only fears XingYi”. It is a statement regarding the overall effectiveness of Mantis styles and also of the difficulty they might have with XingYi’s angling attacks. With a good teacher, you could make either one work very well for real fighting. I suggest you check both schools out and notice if they teach real combat applications along with the forms. That could be the deciding factor for you.