Why not both (aside from annoying potshots at insignificant targets)? Electronic Warfare 1 is probably the most important skill in the game for everyone, mainly to prevent range penalty if the enemy has ECM. If anything, more EW beyond first level is dubious since the enemy may have ECM as well and, being evenly matched or superior to your fleet, will offset your ECM unless you put ECM Package on multiple ships to ensure range advantage despite two evenly matched (or disadvantage for the player) having EW.
If enemy does not have EW, you have an advantage. If enemy has EW, and enough ships to match yours, you will probably be more-or-less at zero regardless of ECM maximum, unless you kill their ships, which by that point, the fight is decided and just a matter of time before you win.