Others have given more in-depth descriptions so I'll just say how I've used these or not. I really recommend looking up the individual objects to make a decision. I always do that in Origin. I look at all the CAS/BB objects and decide whether they add things that I want in the game and whether I want those at the time that I am getting a new pack. I've picked up some packs as bundles.
My First Pet Stuff: I haven't played with MFPS yet because I only recently got it and don't have a reason to yet. There is a nerdy little boy in one of my households who will be perfect for it though, I think, and I have other families. I got this in a bundle recently. It adds small pets, clothes for pets (not really my thing, lol), some kind of nerdy hairstyles and a new death by rodent illness. I probably would have passed on this without the bundle, but I think I'll like the small pets when I get around to adding them. The cage rocket ship looks pretty cool.
Fitness Stuff: I made a really cool gym with this, Oasis Lifestyle Fitness. It is my favorite gym in the game. I really could tear down some of the other gyms if I wanted to or make them over with this. I also like using it to make nice minimalist bathrooms too. I like the climbing wall. I mean, it doesn't add all of the objects that you could have in the fitness theme but it does make nicer gyms. I'd say it's a good pack for builders because it adds some nice natural looking build materials. Yes, it would have been great if the smoothies and other recent self-care ideas came with this pack. I like the video work outs and I use those a lot actually. A new mom can put the baby down and do an impromptu dance work out, for example.
Moschino: I got this and I have a sim who is great for this pack, artsy Ulrike Faust who now lives in San Myshuno. I haven't used it as much yet due to the complaints about the camera bugs. I actually like some of the clothes such as the sweatpants and some other items. Some of my wealthier sims wear them as ways of wearing "designer" clothes. I really bought this for the career and the camera though so hopefully I will hear that this bug has been completely fixed. I haven't fully explored this pack yet.
Toddler Stuff: Do you love toddlers and want more stuff for them? With this pack, I added a toddler park in Newcrest. It's one of the only places that I will take toddlers because I generally like to focus on skilling up toddlers as much as possible while they are in that phase. I only like to take them to places where all their needs can be met. My new toddler park that I downloaded and then edited to suit my sims does exactly that. It also has equipment for kids and a kiddie pool for parents to cool off as well as napping areas, bathtubs and pet areas. The whole family can be together. Anyway, I was able to make that space with this pack. It also allows for many more outfits and styles so that toddlers can all look a bit different. Good for family play.
Laundry Day: Adds realism and as others mentioned, some quirky CAS/BB that is kind of boho/hipster/rustic. Do you want laundry in the game? I didn't care that much and got the pack more for the other objects but once I started adding laundry, I found that I wanted it in most households. I guess I like making my sims need to juggle it on top of other things they do. Strange, but I do recommend it. Sometimes the clothes really pile up. You need to pay attention to how many hampers you add relative to the number of sims. One hamper for a bunch of sims? Expect to do a lot of laundry. The machine breaks and you need to repair it or spend money on it. You can either use washing machines or a washing tub and clothes line. I don't know, I liked making my Strangerville hero stay on top of laundry while she was solving the mystery. Whether you want this is up to you.