Serpent Jewels

I'll say if you have any spare choc, you should clear the most as possible. You never know when do you need which material and event is the best place to save up mat or get the ones you most needed.
Of course if you have limited time to farm due to various of reasons, get the most important ones first

Edit: I probably need to correct myself there, I don't even know you could farm serpant jewel in the current event. If you do able to find it, you might want to check with the drop rate first on the guide on this website, because if the drop rate are too low, might not worth your time

The data from the NA drop rate sheet says it's 142 AP/drop, and looking at the overall drop rates, the best is a Babylon node at 79, and next best is an Okeanos one at 107. Given that this would have to be farmed at an Advanced node in the event (the 30 AP one), I would say it's not worth it. I don't have a lot of data on the 30 AP node's choco drops, but it seems like you'd be losing out on about half of the drops compared to the Royal nodes', and not getting a very good return on the Serpent Jewels from an AP/drop viewpoint. I can't say for certain--if you really aren't looking to buy a lot of shop items, then maybe it's worth it to you to use the event to do both, but using just natural AP regen, you'd only be looking at 2 Serpent Jewels/day, and less than one per apple if you were to go that route (which IMHO would be a very inefficient use of apples).