It's completely up to you. I got the gray ones because I like that dark theme. It feels more adult in my opinion, and blends in to the room better.
If you plan on playing with friends or family, the neon ones might help keeping player 1 and 2 apart easily. Since I'm playing solo 99.999999% of the time, I chose gray again.
Do you like the color? Do you like that the two controllers have different colors, or does it bother you?
You can always put on custom shells later if you want to change it up (I think I would like to do that in the future).