Assuming the use of the advanced EW rules from TacOps, it's a rare game where I don't include ECM, preferably on every unit, and I typically aim to have one Probe per lance/Star, more if I know it's a scenario involving hidden units. Whenever possible I switch the ECM to Ghost Target mode.
In purely TW games, I use fewer ECMs except when fighting C3-heavy forces such as the DCMS and CS/WOB.
I don't really have a 'Mech of choice, although I favor Omnis, especially in campaigns where custom configurations are allowed.