Andrew Macdonald

for sure external or striking styles in show quicker basic results (with a few exceptions) things like karate, with a TKD, muai thai, will teach you effect striking techniques which if you end up in a street fight will be useful. although these are mainly sporting/fighting styles.

another way to go is to take arts which are predominantly martial arts, aikido, some kung fu styles, and japanese ju jitsu. these have strong techniques but sometimes lack in 'live' practice of these applications

with the correct teaching both of these groups could be adapted or included in self defense syllabus, in fact the arts that are know as being self defense arts systema, krav maga include techniques from both the fighting styles and the traditional martial arts styles, but teach them in a different way

so it really depends what you are looking for from your training