I have 16 GGG EI2s on my CP along with 4 Happs. 2 of the Happs are the clears and 2 are the 1 and 2 players (which are now almost "playerless").
I have 6 GGG EI2s for each 8-way, 2 for the dedicated 4-way and one in each "3-cluster" as a left and right mouse button for games like Golden Tee.

The lighting option for the GGG EI2s are amazingly well built little devices. Basically a PCB with a 4-line ribbon cable hanging off each with the common (-) marked in red.
Closeup:

Size comparison:

The PCB snaps into the bottom of the button with a little authority and they don't come loose. They actually sit beneath the swich since the switch is actuated by the tabs surrounding them:

Now, one of the discussions should be customer service. Basically, I wanted to be able to light just blue and set it up for a future upgrade to an LEDWiz (Santa, you listening, you fat bastard?). RandyT suggested putting all leads to a euro-block and jumping the like-colors and picking one to power. When I get my LEDWiz, I will simply make 2 24 wire ribbons and connect them to the back of these blocks, removing these colored wires. It was an excellent suggestion and allowed me to continue with my planned-neat wiring job:

The lighting is interesting. These are my first "milky white" LED buttons, so I found it interesting that in full daylight, the centers of the buttons would take the color of the LED that's currently lit, but the edges stayed milky white:

In the dark, it reverses and the edges become the most colored and the centers begin looking more milky white:

Also, they are bright enough to allow some edge lighting for my CP Plexi:

In terms of performance and knowing I only have the 2 brands to compare, there are significant differences. First, I ordered the GGG EI2s with the standard light-actuation switch. RandyT told me that these switches (along with the actual button design) allow for a lighter touch on the button, eliminating the spike that most other cherry-type switches require and therefor cutting down on some of the fatigue during long play.
I'm not so sure of this, but I will say that these definately require less force to reach the click. But, with this, they seem to be just a bit more "toy" like, where the Happ button and Cherry switch is more of a click. I suppose this is an excellent compromise between leaf switching and cherry-type switching, but it almost feels like the nylon is a bit thinner and lighter. I've never played anything but Happs, so this may just be me. None of the people that play the machine mention it. But, the Happs are definately heavier.
One other issue I noticed was that the switches tend to rattle around in the mounts. After consulting with RandyT, he said just take the switch out, squeeze the two ears together and put the switch back in. I haven't had to do this yet as none of the switches have popped out, just an observation. And, with my wiring, I don't really want to move stuff around if I don't have to:
The multiple switch mount is ingenious. It allows you to orient the button the way you want to, then install the switch mount. They click in with a little authority and have never moved. Putting the nutz on the buttons is much easier than with a solid switch mount like the Happs.
I've had one switch get sticky. There's been nothing spilled on the CP, so I'd imagine its just the switch rattling out just a little.
All in all, these things are amazing. From the PCB/LED to the switch mount, the thought that went into them is brilliant in its elegance. I've not tried using a "standard" GGG button, so I suspect that the "milky white" nylon has to be a little thinner, which makes them seem just a bit more toy-like. With the standard switch, I've had no problems with them for the last 3 months of continuous in-garage 6-pack play.
RandyT is an excellent vendor who really took the time to answer any questions immediately and seems to have a love for this hobby of ours. The GGG EI2s make my CP and indeed, make the machine. I probably won't ever go back to Happ.

YMMV,
AJ