Plot-immunized rocket tag is my general preference. I really like the thematic separation of damage that matters (i.e. it directly contributes to death or disablement) from everything else. When they get mixed together I find it hard to interpret what is actually happening in anything but a post hoc fashion. I'd rather know what happens at the same time the character does. Hit points as a jumble of minor physical damage, proficiency, providence, positioning, preparedness, poise, and luck without other effects are extremely flexible and utilitarian. They can mean almost everything, and so they also mean almost nothing. Thus I find real wounds like "losing an arm" rather jarring if they comes from the same mechanical pool. This separation also makes it easy to adjust the balance of plot protection and rocket tag to achieve the level of grittiness and survivability desired in a given setting.
In the homebrew system I play, one difference from either the basic rocket tag or plot protection systems described in the OP is that neither HP nor defenses go up as characters gain experience, even though attacks do. (This is a success-based system, so there are no separate damage rolls.) Instead, we use a system which gives more "momentum" to characters based on how well they succeed. Momentum can be spent on attacks or defenses, so players tailor their spending to the situation. Momentum also grants access to more powerful weapon maneuvers, and can help spellcasters defray the spell point costs of their spells.
As the PCs gain experience they can mop-up lower power creatures fairly quickly, but these remain dangerous in number and especially in ambushes, because without momentum the PCs aren't much more sturdy than they were at the start of their careers. Against bad guys of similar ability scores and skill most fights are about choosing the right moments to use momentum for defense or attack, and the flow of momentum really gives a sense of the changing tides of the battle. When fighting opponents with very powerful attacks but some notably weak defenses very large swings in momentum are possible for either side, and this is probably the closest the game comes to true rocket tag. Finally, against opponents that have both better attacks and defenses the PCs tend to be momentum starved, which leads to starkly different and desperate combat. In combat with multiple creatures all this combines to create an unusually strong tension (in my RPG experience at least) between the need to focus fire and the need to engage all the baddies so they are not incentivized to pour momentum into devastating attacks. I have found it a very enjoyable dynamic.
