I really like the french link. My 4 year old is ridden in one (he has a soft mouth) and he loves it. You don't get the "nutcracker" action as you would with a normal single-jointed snaffle. The french link lays flat and seems to be a nice soft bit.
I've only tried it with my Paint Horse and he's not a fan for some reason or another. I use a D-ring snaffle with copper rollers that he and my National Show Horse both like. I tried it because I thought the French link would have been softer. So, for my horse it's best to stick with what works.
Around here KK seems to only come in loose ring, and french only in eggbutt, so I use them interchangeably depending on what cheek piece I want. Never had a problem with it! They seem pretty comfortable for the horse.
Lately though, I have been using Myler bits and I quite like them.