I use this one Mikmar Bit Company (got it in Dover). My horse has 5 1/4 size, which is pretty hard to find in config I wanted (double jointed + eggbutt). She likes it over 5 different bits I tried, and this mouthpiece tastes pretty good (yes, yes, I tried it in my mouth ).
BTW, loose rings didn't work for her - she went crazy. Definitely prefers the stability of eggbutt.
Dover Saddlery | AlBaCon French Link Eggbutt Snaffle Bit . decent bit, with some taste, and I used it when I started my horses. They seem to prefer Mikmar and KK Ultra more, but I'm unsure it's because of the taste or the middle link (which is lorenzo vs french), and unfortunately it doesn't come in 5 1/4, so I ended up switching to Mikmar.
I actually have a loose ring, but it's single joint so I wouldn't get a clear impression of whether he likes the rings or not because he'd probably be telling me loud and clear about his dislike of the single joint.