I've played quite a bit of jax (m7)
I usually build 
(circumstantial boots, usually 
) 
(circumstantial item, sometimes tank sometimes 
)
I've seen many people build gunblade 5th and rageblade last. Is this a better course of action? Why?
is more of a burst item. is for extended fights. If you aren't able to stick on to enemies then lets you get off a chunk of burst + a slow
Assuming this is jungle.
You don't build gunblade 3rd? Anyways, it's good for 3 things: stats, sustain, and the active. Gunblade has better raw stats meaning it buffs your abilities more. It gives you good sustain so you can always gank at max HP. And the active slow really helps keep an enemy near you after the E stun wears off or it helps you disengage. Either way, with it you should be able to delete a squishy before the rageblade passive has a chance to build.
Rageblade is better when you need the passive or hybrid pen... so basically when facing tanks/bruisers.
So it really depends on who you are facing.
rageblade is damage (sustained damage at that since you need to stack the passive).
Gunblade is active + healing + hybrid scaling (ap and AD) which benefits a lot of his damage and one thing people forget is that the hybrid stats boost both his armor and MR on his ult, making him that much tankier.
