I have a laughable combat rep, I'm level 108, and I'm wondering, should I go for high firepower and low defence or high defence and low attack? I have nearly 3K hull.

whats your kill/death ratio ?

Halc up and research more hull and attack I recommend.

Kills 24
Deaths 356
I have researched up to Quantum Devastators,Compressed Nexus armour and Phase Shift Engines Mk III

Ouch. You need at least 321 more kills than deaths to get the "Insane" combat reputation.

That's a lot of work for you.

I know, but I'm committed, if it will boost my legion morale then, I'll do it, so defence or attack?

High attack/high hull/high energy when you're online and disabling ships. Get some small scan modules as well, to swap around and change up your battle tab for easier ships.

Switch to high defense/high hull when you go offline.

It's also best to disable in bursts, so when/if you get disabled in return, you're only disabled once for however many kills you have

Thanks

+1 to chiaroscuro's suggestions: turtle when you're offline and tiger when you're killing.

If you want to drop by The Wild Hunt for guidance from some of the best PvPers around at your level, then swing on by sometime.
We love a good comeback story and, if you make a good impression, it might even make our friendly wolfpack less likely to feast on your ship in the future

We're not looking to take you away from your legion, just a short term workshop, comprehensive overview of your ship build and general tune up for your PvP skills.
Way easier to do in legion comm than forum posts.

Regardless, best of luck and happy hunting.

Be the hunter, not the hunted:
Ride with The Wild Hunt

A good defense is to attack, a good attack is to defend.
there's no best in here, it's just a matter of : is your target online? yes = need both high or just avoid.

Low attack = giving them time and opportunity's.
Low defense = need to repair often and they can kill you before you kill them (think suicide run)

What modules do you have when you are online, and offline? A picture of your ship might help.