The button (as per Evan's installation) has the advantage of a quick press to engage it. But it has the disadvantahge that you have to drill holes in your dashboard, and is altogether more difficult to install.
The headlight version is the cheapest, but changes the functionality of your headlight flasher. (You can't flash your brights if the headlights are off, and engaging or disengaging EV Mode via the switch flashes your brights if your headlights are on.)
Costal Tech's switch on the cc stalk has no effect on the functionality of the cruise control, and is the easiest to install. (A beta-test version prevented cruise below 35 mph, but that problem was corrected.) But it has the disadvantage that you have to hold the stalk for 2 seconds (really seems like 3 to me) and since the cc stalk rotates with the wheel it's hard to reach if you are in a turn.
I have Costal's switch and love it. I'd have prefered Evan's solution if I was really handy with tools.