I feel like Thrawn is a militaristic genius, his people (based on lore) had infiltrated all of the major factions during the clone wars. I wouldn't be surprised if he had more knowledge of the empire's weakness than what the even emperor knew.

Thrawn is definitely the smartest and most dangerous, but Moff Gideon is the most ambitious, from what we saw. Not to mention Thrawn makes the most out of the tools he has, while Moff Gideon seems to get a new tool and tactic every time he appears.

Well, Thrawn has already been established as one of, if not the, most intelligent officers the Empire has. That being combined with his tactic of learning his adversary inside and out (watch Rebels for an example of this) make him a highly dangerous foe. Most likely, he knows your next move before you even do.

I say that Grand Admiral Thrawn is more intelligent and dangerous than Moff Gideon is

Thrawn studies you to know your next move, Moff Gideon makes sure you only have one choice so that he can finish you there. Gideon was able to do a lot with what little resources he had, while Thrawn has one of the largest fleets in the Empire. But when it comes to just the two of them alone, Thrawn makes a plan based on what he knows you will do and goes straight to the point when the time comes, while Moff Gideon will make sure your only choice leads you to a trap. Well, so far that's the only thing we've seen Moff Gideon do, while Thrawn would probably do that too.

They're both pretty well-balanced, honestly. In a fair fight Moff Gideon would find a way to make it unfair, while Thrawn would straight up just win because he's superior in basically every way.

Yeah, Thrawn studies his foes, so he knows his enemy's weaknesses. I think in comparison to combat in this modern age, knowing your enemy and how they’ll fight is vital before actually engaging in combat (example: American CIA)