Spa Day or Jungle Adventures?

I think JA is much better and brings fun content to the game.

You are talking about 2 completely different game packs. Depends on what adds more fun and content to your gaming experience.

Hmm...
On one hand, Jungle Adventure has a lot to do, places to explore, artifacts to find, sights to see.

On the other hand, without the Wellness skill from Spa Day, you can't teleport around the jungle, and the jungle is really big!

I'd say get Jungle Adventure for now, though.
It's a fun vacation destination, and I also like the new radio stations is comes with.

As entertained I am by the concept of Jungle Adventure, I had to go with Spa Day. Not only does it add the new Spa venues, it also adds a host of other content I tend to use in game on a daily basis.
It adds the wellness skill, which can be built by doing several things - yoga on the new yoga mats, meditating on the meditation stools, or giving massages on the massage tables and chairs. If you choose to go the meditation route, you can actually freeze your needs while meditating once you get high enough, and you can also unlock the capability to teleport at will.
Then there's a massive supply of moods you can get your Sims into super easily. Different yoga routines will give you moods, as well the new mud bath and various perfumed bath options you can perform in any tub. There's also a new music station, New Age, which focuses any Sim who's listening to it.
I really like the pack, and enjoy the spa venues that I can send my Sims to when they need to relax. It's something I use repeatedly across all families.

I like both packs, but Spa Day just adds so much more things to enhance your Sims everyday life. You probably don't want all of your Sims to become Archaeologists or Adenturers or even take them on regular vacations, but Spa Day has something for every household, even if it is just a scented bath. I won't go into any more detail because @TheGreatGorlon already did a great job - way to live up to your name. :)

I love all of the lush jungle scenery and turning into a skeleton is the best thing ever - one of my sims had me dying the other day with the sound of their bones jangling as they walked around (:

I've had a lot of fun with the jungle. I already have a ton of laundry, but I'll probably never get an archaeological adventure, so this one's my pick. It's been entertaining to explore the ancient area, and you get a machete. Plus new food. The puzzles aren't hard, but the results can be super funny, especially the curses. Someday I might get laundry on a sale for the build items, but the jungle is awesome--oh, hey, my dryer is buzzing irl...

I use both regularly, so it was hard choosing. Either one is good for different things.

Spa Day might be better if you prefer realistic gameplay, but otherwise I'd suggest Jungle Adventure first.

I bought Spa Day because I felt I could use more of the stuff from that pack and I was right.

This was a tough choice for me. I love both of these packs so much! I only just received JA as a Christmas present and I'm still exploring everything it has to offer. So, I've used everything in Spa Day much more than JA at the moment. I love everything about that pack and use the items in just about every household. But, JA comes with a new vacation world that is absolutely gorgeous! Spa Day doesn't and since JA is new to me right now it's my current favorite of the pair. You can't go wrong with either one in my opinion. :)