Nether or both.
The big trap in the survival of the fittest is that fit doesn’t have the traditional definition of fit. It gives the impression that its a competition to be the most successful species which it isn’t, it’s a fight to be as selfishly successful as possible.
This means their is a variety of strategies and interaction that will evolve.
Some do seem confrontational, like the relationships between predator and prey is largely a competition. Cheetahs need to run fast to catch gazelle and similarly gazelles need to run fast to get away from cheetahs, but in both cases the objective is not to have cheetahs be more successful than gazelles or vice versa, it is a pure selfish objective to be as successful as possible.
But in situation were two species can bring something the other doesn’t have improving resource collection, then it is in the best selfish interest of both species to collaborate and eventually form an inseparable symbiosis.
Sometimes it is the species best interest to give something a way, that is the reason plant produce nectar and fruit. It give animal and insects a selfish interest in passively carrying their seeds and pollen to new areas with more ressources.
This does also mean that their is a competition between two species for a same limited pool of ressources.
So sometimes it is a bloody struggle, sometimes their is cooperation and sometimes their is something that may look like altruism but is more similar to a salary than a free gift. Ultimately it is all selfishness, millions of selfish species interacting balancing ou in the environment.