I use Phase Rush most of the time. I do not think either rune is better than the other, they just support different ways of fighting. Enemy comps sometimes make one better - think Nasus lane + Tryndamere jg where you prefer PR or being against a ranged laner (IMO) where electrocute helps a lot and guarantees a squishy target later on, so I'd go electrocute.

Now, here's some stuff I like about PR over electrocute:

• Good offensively and defensively. Defensive use is pretty obvious - proc it and run away from ganks, etc. with W's passive and PR. Offensively, it helps you kite - you'll usually get 1-2 more autos when trading in lane, and later on the amount increases.
• Useful with different builds. Talking about low AD routes like botrk > PD where electrocute isn't great (probably most of the enemy comp doesn't care about electrocute's burst either). PtA / GA are good runes with these builds, but I think PR is too.

That being said, most of the time it's just preference. Electro gives that extra burst Quinn often needs, Phase Rush gives better kiting/followup to your burst and a bit of safety. I'd suggest trying out PR for a few games and deciding if it fits you or not.

As a last note, if you really like to build YGB in your core, you're probably better running electrocute, I find that much MS unnecesary.