I dont run an "active" task manager, because, as been discussed over and over and over, they consume resources themselves, contribute to bad battery life, etc etc etc.
However, i run System Panel Lite on all my phones. Its not an active task manager, doesnt run in the background. Its a killer, basically. You can choose what level of apps to kill, forground, background, system apps, etc.
I excluded all the apps that i dont want to ever kill, then put the "kill all" 1x1 widget on the home screen.
When the phone starts to lag, or right before i'm going to start something that requires extra resources, i just hit the kill all widget.