It is often asked "What's better for fighting: MMA or Jeet Kune Do?" But in fact, this question is inadmissible since it aims at comparing two things that are chosen from fields which are by far too much different from each other to allow for a direct comparison.
Whereas "Mixed Martial Arts" (MMA) is in fact a fighting sport (with different branches), Jeet Kune Do (JKD) is in fact a combat system (or "framework", to comply with the concept and terminology used in several branches).
Note that, in the given context, both MMA and JKD should only be regarded as arbitrary representatives of fighting sports and combat systems, respectively.

The purpose of a fighting sport is to find out who is physically superior by competing in a safe environment with rules that exclude any techniques that are likely to kill, seriously harm, or cripple the opponent.
The purpose of a combat system is to successfully accomplish a combat mission or at least to survive an attack by applying the appropriate most effective techniques without caring about killing, seriously harming, or crippling the opponent. In military and related scenarios, killing the opponent is often even the explicit goal.

Therefore, fighting sports and combat systems differ completely in the underlying mindsets as well as in the scenarios they are created for. This means comparing fighting sports with combat systems is very analogous to comparing a particular tactics in the board game chess with a particular tactics in the battlefield of war. Of course, there are analogies and formal similarities, but a direct comparison would mean the following:

When the hostile soldier is jumping towards you, aiming at your face with his loaded assault rifle, just about to pull the trigger, you will pull out your chessboard in order to invite him to a game, and, vice versa, when your opposing chess player is just sitting down at the chessboard in front of you, you will pull out your submachine gun and blast his head away...

Although both is actually possible to be done, it does not really make sense for a comparison. And it wouldn't make more sense to put a JKD guy into an MMA ring, or to put an MMA guy into a JKD-style street fight. - What would happen?

- In the ring: If the JKD guy does what he has learnt, he will have much more effective tools available and blast the MMA guy off, but then, he will be disqualified and expelled from any sports organizations, and probably also be thrown into prison. If he tries to comply with the MMA rules, he will have to suppress all of his conditioned reflex responses, thus paralyzing himself while being blasted off by the MMA guy.
- In the street: If the MMA guy does what he has learnt, he will restrict himself to ineffective acting and will be blasted off by the JKD guy, but if he tries to free himself of complying with rules, he will enter a field he is not familiar with and thus be blasted off by the JKD guy, too.

The conclusion is simple: Fighting sports and combat systems only work within their corresponding environment; using one in the environment of the other will fail. If you want to succeed in the ring, go for a fighting sport; if you want to succeed in the street or in battlefield, go for a combat system (or at least a self-defense system). But never try to cross-compare or to interchange them...