What's the most advanced SIP client for Linux these days? [closed]

I'm currently struggling which SIP client software to use with respect to Ubuntu / Gnome. Some clients I've looked so far:

• Blink, seems promising but the Linux variant lacks a lot of features
• Twinkle Latest release is ~2 years old. AFAIK the only one capable of encrypting calls using zrtp.
• Empathy: default tool for IM on ubuntu
• Ekiga

Some features I'd like to see:

• availablity of buddies
• conference calls
• call log
• chat
• desktop sharing (Blink seems to do that for Mac)

So my question is: what client software do you prefer and for what reason?

To get a deep analysis, let's look at the Ohloh entries for each item on the Wikipedia list:

• Empathy (Telepathy-Rakia)
• Jitsi (formerly SIP Communicator)
• Ekiga
• LinPhone
• Qutecom
• SFLPhone
• KPhone
• Blink: I added the project, but Ohloh can't process Darcs repositories yet.
• Twinkle: Can't find a publicly available repository.
• PhoneGaim: No longer available

Based on what I'm looking at with all of these, I'd limit further research to the first four. (I've more-or-less sorted these by their reports, but those need some more in-depth digging.)

Ohloh only allows comparison of a maximum of three products, so here are two comparisons. It's probably better to move these around yourself though, and actually run these things to compare their features. I'll be doing this myself in a little bit.

• Comparison of Empathy, Jitsi and Ekiga
• Comparison of Jitsi, Ekiga and Linphone

Hope this helps!

Betraying my ignorance, I'm going to link to the Wikipedia list.

Some you say you haven't tried:

• KPhone
• LinPhone
• PhoneGaim
• Qutecom
• SFLPhone
• SIP Communicator

You might try looking at the crossplatform clients first (bolded above), as I have a hunch that they will be more developed.

To install Blink in Ubuntu 12.10.

$ sudo -s 
password
$ cd /var/tmp
$ wget http://download.ag-projects.com/agp-debian-gpg.key 
$ sudo apt-key add agp-debian-gpg.key
$ vim /etc/apt/sources.list
# add those on top 
# Ubuntu Quantal
deb    http://ag-projects.com/ubuntu quantal main 
deb-src http://ag-projects.com/ubuntu quantal main
:wq
$ apt-get update
$ apt-get install blink

Run the blink.