All of them of course!

Why go in half measures? With the very extinction of their species on the line they decided that it was best to take no chances. With the decision made the remaining Fluidians altered themselves into a virus that would be harmless to humans, but would cause a definite number of changes to their hosts. Loading onto the comet and launching at earth was the first step into the unknown. The Fluidians were a kind species and realised that they would need to change a few more things about the biology of their hosts if they wished to have a truly symbiotic relationship. These changes were truly up to the individual Fluidian, even if they did agree that it should be all fluids.

As the comet passed through the atmosphere and began to break up, the Fluidians said their farewells and best wishes to their brethren. Though, if all went to plan, they would one day be reunited with the cloned offspring in another infected hosts body. Speeding over the planet each chunk of debree fell somewhere different but the piece of infected rock were following in this story lands...

(readers remember: from here there are multiple customizable names that I, Kingsy, will include. Change them to truly make this story your own)