I have practiced both and recommend both. Krav maga is a bare bones take them down, street fight, while MMA is more of a subdue.
Another good MA is aikido( which I have practiced as well).
The thing is, PSHTF ( or even now) you don't want to have that frame of mind of beating the crap or killing everyone who crosses you. You want that survival mindset of surviving with the least amount of force and damage as possible.
Whether it's a person or animal, you want to discourage them from messing with you, preferably without hurting them ( or you getting hurt).
The good thing about MMA( Ju Jitsu) is you can wrap them up until they calm down or choke them out and leave.
The thing with Aikido is you use their force against them. Watch youtube vids on it and see how they do it, it real and pretty easy to learn. When an opponent comes at you, you sidestep and make contact with them and go with their forward motion, then trap them and take their motion farther( in the same direction), taking them off balance, then suddenly you change direction, do a 180 and take them down quickly and there's nothing they can do about it.
That's if you want to be nice. If not, then you do the same-sidestep, go with them and then suddenly clotheline them in the throat with the front bone of your offhand wrist or near elbow.