For bike-to-bike communication nothing beats GMRS for range and clarity, however as you know it involves a lot more complexity. GMRS requires a power source, and something like the Autocom with PTT. Only GMRS has the range and reliability to communicate with riders out of sight, and even up to several miles. For example if someone passes cars/trucks on the road, they can call back if the road is clear or traffic is coming. A BT will be out of range quickly.
Any BT solution will be limited to line of sight, or at most 1000 feet, although uClear uses a short-hop technology that can extend that through multiple headsets, and the Sena 20s may also have their implementation of that technology. The short-hop falls apart as soon as any two riders exceed the range to maintain connectivity. The biggest problem is the BT headsets are not very compatible between brands. So if your friends use Sena, get a Sena, if they use uClear, get that. The functionality is roughly equal, but uClear uses a jaw mic which does not require a boom and mic in front of your mouth, while Sena uses a conventional mic. BT headsets are limited in the connections they will make, and none will deliver both GPS and Radar Detector.
My solution is to use the uClear for music, GPS and phone using earbuds from uClear with built in jaw mics, with Autocom for GMRS and RD through helmet speakers. That gives me the flexibility to intercom with other uClear users and have the GMRS for longer trips and range, and I have a backup if either unit fails or the BT loses battery power (about 10 hours). IMO a Sena could replace the uClear very easily except it would require a second boom mic. More FJR riders seem to use Sena than uClear, so you are more likely to have someone to talk to with Sena. Very few riders currently are using GMRS.
Bottom line, there is no single best solution that works for everyone.