Packet Analyzer

Is there something like packet analyzer for minecraft that would tell me which packets are used most?

On our server we have occasional problems where people (especially ones with bad internet connection) are getting randomly disconnected, sometimes very frequently. Vanilla server works fine, so it's not the connection itself.

Now we would like to figure out, which packet is causing most issues, so we can pinpoint which mod causes those issues.

Try asking on bukkit forums?

Its vanilla server, it have nothing to do with bukkit.

If you're willing to read about this stuff, this could be worth a try:
read up on Wireshark (download it here) and check this plugin for it: http://www.highprogrammer.com/alan/games/video/minecraft/minecraft-dissector.html

It hasn't been updated for 2 years, so it's likely to be totally useless by know. But depending on the information you're seeking for, it could still be worth a shot.

I have found little mod called McPacketSniffer: https://github.com/bencvt/McPacketSniffer. It's interesting.