User blog comment:Inquisitor dusk/tyranids vs flood/@comment-5131965-20130225031110

I'd say, and this is my personal opinion, that the flood would have the upper hand. However, the sheer genetic adaptablity of the Tyrannids could make their forces immune to conversion.

Another thing, is that Flood can only assimalate intelligent life forms; most Tyranids, other than the larger monsters, have an intellect composing of

1: doing what the hive mind tells it to do.

2: do what the Hive Tyrant tells it to do.

3: eat anything it comes accross.

4: if cannot eat enemies, fall back, and call for reinforcements.

5: breed (minor rate in comparison to Hive Queens, though does explain the Fenrisian Kraken, Catachan Devil, Scoria Chiten and many other Tyranid species accross the galaxy)

another thing is that both use, once they are able to acquire these materials, is raw biological matter. Tyranids use this to create (through Hive Queens) more Tyranids; and Flood use this to create the Gravemind (which is like a physical manifestation of the Hive mind).

The only race that neither of these races could fight, and win against, in warfare, are the Orks; Necrons; and the Imperium of man (to an extent)