Both are great damage dealers, so the answer to this question is who do you prefer more. Ray has weird range and an... Interesting ammo mechanic, while typhon is more of a general dps who can shred bosses and tough enemies as long as she gets to shoot at someone 5 times, which can be achieved pretty damn fast with her S3. Some meta enthusiast is probably going to give you a clearer answer. I'd personally go for Ray, but typhon is also a great unit.