What stuff pack should I buy?

Depends on what you're looking for, but if you want a new pet and/or new death (that works on vampires too!), MFP is a good choice. VG's good if you want the butler. Either one will give you the most for your money.

The other packs are good too, but more situational/niche. The big ol' slides from Backyard will probably end up on a community lot you only go to once in awhile (they're good for water parks, for example), and obviously Luxury Party stuff only really gets used if you throw a lot of parties, or again on community type lots (or builds like orphanages or nursing homes or something).

Just my thoughts, on those options.

really depends on which you'll get the most out of. I own all of 'em and they all get used for the most part. LP and VG have great CAS pieces and LP's buffet table sees a lot of action at parties I throw in-game. VG's butler and vanity is cool but don't see too much action in my game but the bedroom set gets used in my more extravagant households. MFP is rather niche so unless you really want the tiny critters and/or to complete the kids' bedroom set, I'd say opt for something else. backyard really fills out the outdoor furniture category but clothes-wise didn't blow me away. BUT if I had to pick. . . probably Luxury Party overall. if you play with a lot of children and stuff, MFP and Backyard are your best bet.

I love everything in VG. I don't own Backyard but it's #2 on my DLC wishlist (behind Parenthood) so I'd likely recommend that one too.

Oh that's another thing about MFP! If you have Kids' Room SP, Toddlers, and/or Parenthood, a lot of the furniture really works with the younger Sims! :)

Backyard is the best one in my opinion of course I have them all. Backyard adds bird feeders,lemonade pitchers,waterslides and windchimes.

Thanks guys! I still haven't decided yet, I'll be purchasing the pack later tonight. Vintage Glamour seems really nice, previously MFP and Backyard were my front-runners but now I'm not so sure! I really appreciate the feedback on the quality and usability of these stuff packs.

Vintage Glamour seems to be doing best, and it does look like a really nice pack. They all look so nice though!

CAS: Vintage Glamour > Luxury Party > Backyard Stuff > My First Pet

BB: Vintage Glamour > Backyard Stuff > My First Pet > Luxury Party

Gameplay: Vintage Glamour > Backyard Stuff > My First Pet > Luxury Party

The results are in...and I think we have a winner!

All of them.

I never judge a stuff pack by their gameplay since it's always so restricted, they usually come with one main gameplay feature.
I always look at the build/buy items and cas items and by that, Vintage Glamour is the best imo and beats all the other stuff packs. It comes with some unique and beautiful furniture for bedroom and living room. CAS items are also very nice.
Gameplay wise you'll get the butler and an interactive vanity table. Butler can be useful for your rich sims.