Salim
As you know both clients are trying to solve different use cases/work styles. There is some points of intersection of course. Jabber is more for your ad-hoc IM/P, classical available/busy presence states. Spark is more activity based presence, are u online, have u used the client in the last 10 min, 24 hours or more
Spark was written mobile first easier for file shares/transfers/flagging and search filters. Jabber is PC centric ported to mobile too but needless to say over MRA specifically file transfer needs MFT turned on and persistent chat rooms aren't built for mobile like spark
UC is where they differentiate the most. Jabber is heavy telephony centric, park/pickup/transfer/conference/H Log. Spark is simple desk phone control and soft phone with answer/decline and that's it. Maybe in the future some cases might like conference(where today u can but within spark clients vs PSTN numbers). desk phone control is coming for CUCM endpoints, today only spark reg clients
Sharing in Jabber works even on IM without a call vs Spark that needs a call established first but needless to say sharing will be enhanced even more in spark M2 plan down the road
Spark will have more tighter integration than Jabber for joining meetings such as fast join into a meeting, see who is in the meeting before going into the space and many more enhancements planned which can't be discussed here
Jabber has emoticon support on desktop vs spark
Both support SIP URI dialing to call other video endpoints and receive content share. Spark proximity on the other hand has more features and easier to get working and supports moving of calls. Jabber has no concept of proximity.
Jabber through UCM can talk to H323 endpoints too via and can handle IP dialing but spark cloud is pure SIP dialing unless u bring in a cloud services like CMR to bridge disparate protocols.
Hope this helps, mark them as answered or helpful please
