You forgot to include the Necromorph from Dead Space. In a fight between all four species, the Necromorph would most certainly win for several reasons.
1.) Unlike the Flood, it can infect life forms of any size.
2.) It is very intellegent, capable of formulating attack routes and strategies.
3.) Many of its infected forms also are capable of ranged attacks, making them lethal from any distance.
4.) It is capable of rapidly changing the environment--this includes everything from making floors sticky & slowing down its opponents to changing the air into poison.
5.) It has Leviathans.
6.) It can "play dead" for long periods of time, then reanimate and attack without warning.
7.) Some of its infected forms are invulnerable to all conventional weaponry.
8.) Some infected forms release hordes of tiny crawlers which latch onto an enemy en masse, quickly wearing down its defenses and killing it.
9.) It can adapt its infected forms to suit its exact needs.
10.) It uses psychological warfare to wear down its opponents before it kills them.
So yeah, the Necromorph would win.