I did taekwondo from grade 1 to grade 6, leaving the sport as a red belt (decided not to continue when I moved to HK). In 2014 I spent a few weeks doing some Systema (the martial art used by Spetsnaz GRU, Russian Special Forces) but having since been busy with university I haven't had time to continue.
I'd very much like to do Systema regularly once I have more free time, I find it much more applicable to real life fighting scenarios (making use of the body's natural biomechanics, knife training, weapon disarming techniques and exploiting the body's areas of weakness) as opposed to taekwondo's style of fighting which is centred around a structured style, competition and scoring points in arenas rather than street fighting techniques.
It's funny, we actually spent a whole lesson on the ground being taught how to counter opponents with BJJ experience.