I like Soundwave more than Bumblebee because he can have conflict with Megatron's other commanders, but he just seems more like an accessory to Megatron than his own character with his own motives like the other 3 main decepticons.
Oh voice, not voice actor. In that case, I'd say the pitch in Soundwave's voice was certainly higher than the other decepticons but it was probably made that way to go with the cassette tape aesthetic.
If I were to call anyone of them genederless it would probably be Shockwave as he's hyperanalytical, devoid of emotions, and doesn't socialize. Pretty much just a robot.