I am at the GP this weekend.
IMO the Ferrari is the sweetest sounding of the three engines. The Merc is harsher, like a poor after-market exhaust, while the Renault sounds quite soft. Can't say what they are like on TV, as I haven't really seen them.
The Ferrari is incredible under braking. All three have the turbine like whine, but the Ferrari has no exhaust sound, and the gear changes are imperceptible.
When they get on the power, all three growl and grumble, before clearing out to their final note.
The Renault is clearly the least sorted. Lots of surge on partial throttle/low speed running. RR seems to have the best situation, perhaps they have the latest software and the others don't.