In terms of how interesting and developed they are:
Applejack's, because... well, mostly because they're the most developed, but they're funny and have some great designs.
Pinkie's, because Maud, and because her other sisters also have fantastic potential. I also love their designs.
Fluttershy's, mostly because of design. I really like how distinct they all are, yet how they're clearly related.
Rarity's, because her relationship with Sweetie Belle is really interesting, and their parents' designs are at least unique.
Twilight's, because although I love Shining Armour, Cadance and Flurry Heart, I definitely feel like Twilight's bond with Shining Armour still needs some work. And their parents... are kind of boring.
Rainbow's. They were pretty one-dimensional in the episode we saw, so here's hoping they get some more development in future.
But in terms of most supportive, etc:
The Apples again- they're so close-knit and really care about each other. Though they do argue, there's clearly a lot of love and trust there. Definitely the kind of family I would love to have.
Twilight's; her parents are supportive of her studies and she seems to have a great relationship with her brother. Her sister-in-law is also one of her oldest friends, and her niece is shaping up to be the most powerful pony in Equestria.
Rainbow's. Honestly, I was pretty eh about her parents. They mean well, and their support obviously did wonders for Rainbow as a filly, but they seem to stress her out a lot, and I didn't like how the show made her frustration with them seem like something mean and unjustified. Viewing your kid as a platform for their achievements is kind of weird.
Rarity's. There's no reason to believe her parents are neglectful as such as of yet. They definitely need more development before we can know, but their absence is strange and I'm sure looking after Sweetie Belle alone takes a toll on her.
Fluttershy's. They're not bad ponies, but as a unit they seem just a little dysfunctional, probably because of Zephyr.
Probably pretty controversial, but in my opinion, Pinkie's family is the worst. I get really bad vibes off her parents. Maud is wonderful, but Limestone and Marble don't seem as friendly and open with her, and I get the impression there's some tension there, and that's not surprising. A rock farm doesn't seem like a great place to grow up.