Most modern road bikes have brifters - integrated brake and shift levers. These are made by brands like Shimano, SRAM, Campagnolo, etc... My Cannondale has Suntour shifting. It is not compatible with the other brands. Suntour closed up shop in 1995. They were small and couldn't compete with the giant Shimano, though their quality was arguably superior.
After taking the new Schwinn on a couple of rides I came to a surprising conclusion. The bike is a pleasure to ride and its Shimano 105 gearing shifts well, but...not as well as my 20 year old Cannondale's Suntour. What little research I have done revealed that Suntour does indeed shift more precisely by design but is more likely to be finicky about being properly adjusted. Maintenance requires a more diligent mechanic. In the decades of ownership, however, I don't recall ever having adjusted it apart from installing new cables.
Shimano, on the other hand, is less precise in shifting but is more forgiving when it comes to adjustment. The shifters on the Schwinn remind me of the Rapidfire shifters on my mountain bike in the manner of operation. It is a nice setup, don't get me wrong. I can't say yet one system is better than the other. They are simply different.
The only downside to my Suntour shifters was the mounting location. In the early '90s downtube shifters were the norm. Shimano and Campagnolo introduced integrated shifters at some time in the '90s, not long before the demise of Suntour. The downtube shifters work really well but at times can be inconvenient. Shifting requires moving the hands away from the handlebars. When riding in large groups I prefer to keep my hands ready for braking and making evasive corrections.
I always wondered what would have happened had Suntour survived. One day I stumbled across something on eBay that hinted at the direction they were taking. Instead of being integrated with the brake levers the shifters are mounted on the handlebars just above the brake levers. The mechanism actually sits right alongside the brake hoods so shifting can be achieved from the hoods, and supposedly from the drops as well. They look like big wing nuts, which I like because it is a bit different from everyone else's gear. I found a set and installed them but the weather has not been conducive to riding lately. I can't wait to get out there and take them for a test run.
They were a little expensive. I found them online, NOS. 17 years old , never even installed before. Of course rarity can make thing cost more but there is also another reason. Cyclocross racers like them. Unlike other shifters on the road, Suntour's shifters were switchable between indexed and friction shifting. In indexing mode they only really work with Suntour gears, and not all of them. But when switched over to friction mode they will work pretty well with just about any gears you might have. The downside is that the rider has to move the shifter to just where it needs to be. The indexing is what sets the proper positioning on most bikes today. The CX racers like them because the levers are convenient to use, yet their location protects them from accidental shifting due to bumping into other riders and crashes.