With the movement to 1x drivetrain setups, I’ve found it difficult to find a bell that mounted to my cockpit in a way that was easy to access and ring, without taking my hands off the grips or having to unwrap my thumb, etc.
Previously, I had used a Mirrycle Incredibell Brass Duet Bell (~$10 from Amazon; Warning: if you get this bell, be sure to buy from a REAL bicycle shop such as “Trail This”, as many of the ones listed are fakes made in China ~$2, while the genuine product is made in Japan).
I mounted the Duet bell upside-down on the left-side, situated where my index finger would normally hit the release trigger for the front derailleur shifter. In this position, it worked great and was very ergonomic. I could also keep my hand/thumb firmly wrapped around the grips. The bell also has a very loud and long ring tone, which rings both on the initial push and also on the return of the lever, so 2 pings per push (“Ding-ding”!).