You should be making your defensive ship an 'escort' and your offensive ships 'capital' even if their tiny!
I usually use the jammer that dousn't use a resourse, but in all honesty i have not observed that it seems to make any difference at all? Probably when combined with some of the support ship jammer modules it is better?
The main reason i use it at all is Because the defensive modules are damn nasty on the build time, very nasty,,, so anything else that ads 'something' to defense while shortening the build time, is worth it!
I forgot to explain... i also usually have a support ship in every fleet. I will put all the useful 'fleet effect' modules on it. Most commonly i build support ships that use fleet effect modules that do not use a resource... these modules are invaluable. The space left over will hold carrier modules as the priority, if i don't have or not enough space, then weapons. Again although it is a support ship, if it has any weapons at all, you should set it to Capital. I will build lots of these for defensive fleets.... defensive fleets never use anything that requires a resource, that's my rule. All the resources are put towards a small number of offensive fleets.