I've stayed out of this FE discussion for a while, and I beleive that it's pointless to discuss what is the "Best" front end. I know from experience that designing, coding, testing and deploying any piece of software can be a major challenge.
My hat goes off to ALL the individuals that create and maintain free FE's for the public. It's a tough job. When I made Kymaera open source, I was hoping other programmer's would pick up the project and help relieve me of the day to day coding tasks.
As stated somewhere above, Kymaera has enormous potential to be a great frontend. I simply just don't have enough time to work on the Windows, DOS, and Linux versions.
I'll put out a release sometime soon that fixes some of the more glaring bugs, and I'll add a few new features such as sub-menu support, and moving images(ex: AtomicFE), as well as a redesigned setup and skinning application.
Overall, I'm very happy with the features in Kymaera.
For those of you who don't know, Kymaera features:
1) full screen, non-windowsy look
2) completely skinnable
3) multiple Emulator support
4) remappable keys, mouse, joystick support
5) horizontal and vertical support
6) Windows, DOS, and Linux versions
7) multiple lists of games, you can mix games from different emu's in a single list

a "wheel" game previewer
9) support for catver.ini, advanced game list generation tools.
10) a few dozen other common features.
The biggest thing I'm lacking at this point is good doc's on how to use all this, as well as a more skins and emulator config files.
I would really like to distribute Kymaera with more pre-configured emu config files to help people set up thier cabinets.
I haven't seen any features listed in this thread that Kymaera can't already do.
People just don't seem to be using Kymaera, or if they don't, thier not talking about it. According to the statistics at sourceforge.net, I still get a few dozen downloads a day.
Maybe if I heard about more people using it, I'd be more inclined to make more improvements.
just my .02$
-PMF