Rope Climb: To me this obstacle represents what I love about obstacle course racing. It tests you but with practice it gets easier (perhaps one day it will be easy). The rope climb is usually at the end of the Spartan, so by the time you get to it, you're tired. Or maybe you're a super hero and you're not. Anyway, I love teaching this obstacle because it's technical. Yes, you need some upper body strength and grip strength. But by mastering the S- or J-curve, you can leverage your lower body and save yourself 30 burpees.
Rings/Monkey Bars/Multi-rig obstacles: I have spent a good amount of the past several months working on my grip strength to conquer these types of obstacles and I'm so excited it's paid off. It's such a great feeling to conquer these kinds of obstacles. Putting in the training takes discipline but it's worth it when you don't have to do burpees. I don't always conquer them (ahem, Funky Monkey) but at the very least I can get pretty far.
Hercules Hoist: To me, the Hercules Hoist obstacle is one of those that isn't for the weary but isn't that hard. When I would still do my regular HIIT workout and show up to a race, I was still able to beat the Hoist. I can see this being challenging if you're not doing some sort of strength workout, but it's always been an easy win for me.
Cargo Net: The Cargo Net is a great confidence booster. It's easy, although I suppose if you don't like heights you may not like it. But if you don't like heights, there are probably a lot of obstacles you don't like...
Balance obstacles: Balance obstacles are a good way to assess your core strength. If you're doing plank work or some other kind of core work, this should be a pretty easy obstacle to beat.
What are your favorite obstacles?