I'm somewhat of a Flash loyalist, but I'm in the minority. I've always preferred Adobe Flash over HTML5 because it performs better on certain metrics and I do not care so much about battery life so much as rich content like the Unity web player offers as of late. Security has never been an issue for me because I make sure to always use the latest versions of software and I use tools like NoScript.
I'm disappointed that Adobe didn't fully stand behind their product or had put in more effort to have it be able to directly compete against HTML5 when that came out and eschewed Apple's anti-Flash policy and went on ahead with making a mobile version anyways. But maybe this couldn't be done, or Adobe decided there is more money in the approach they're taking now.
Regardless, I will always download and install Flash so long as Adobe keeps coming out with newer versions of it. I would rather have it and not need it than to need it and not have it. It is simply put, the more matured technology. HTML5 I will like much more when it is fully fleshed out in terms of web games and video.