for general self defense purposes or MMA purposes?
for MMA:Sambo Muay Thai
for self defense:Krav Maga Sambo
sambo is a military art founded by the USSR and is very effective for both self defense and MMA purposes. it is the best single art to incorporate both striking and submissions as well as incorporate good take downs and transitions. the way Combat Sambo is done is very similar to that of MMA. Just look at how well Fedor transitioned into MMA from Sambo, as well as Aleks, AA, Megumi Fiji
, Kharitonov and Oleg. i think that it is better then JJ for MMA purposes and is the best art to for a well rounded game. Muay Thai strikers have also done very well in MMA and from personal experience the striking transfers very easily. the 8 point striking of Muay Thai makes it very effective and resourceful and is imo the best art for striking. There are a lot of notable Muay Thai fighters in MMA...in fact too many to name even half. just for reference, Anderson Silva, Shogun, Wandy, Thiago Alves and Kenny Florian have all used Muay Thai effectively in MMA.
I already explained Sambo but Krav Maga is just vicious. look --->Here<---
and see for yourself