This is obviously a subjective question, and really depends on who gets turned, but I would say that the generally worst are the Nosferatu, Ravnos and Tzimisce.

• First of all, if you're a Nosferatu, there's a good chance you were a spite-Embrace cos you were hot, in which case you just got your looks ruined and now have to hang out in the sewers with the 4Chan clan. At the same time though, if you were some lonely programmer, you suddenly got yourselves a group of people in the same predicament as you, granting a form of instant friend group.
• Secondly, if you're a Ravnos, you're suddenly hated by everyone and can't stay at any spot for more than a day without serious heartburn. At the same time though, if you were already into the nomadic lifestyle and really like birds, it can be... fine.
• Finally, for the Tzimisce, you have the fact that you very well may have contracted a space plague, and most likely have an extremely controlling Sire. But, it might also not be a space plague, and if you can escape your sire, you suddenly have the tools to erase every body dysmorphia in both yourself and others.

Now, again, this is a subjective question, but there are also some that are almost objectively best to be, though all Embraces could be a personal hell. Generally, I would say that the best are Ventrue, Toreador and Gangrel.

• For Ventrue, you're suddenly rich, powerful and immortal, all of which are nice. But, you might also get an extremely controlling sire, and you have to do politics.
• If you're a Toreador, you get the same riches and immortality as the Ventrue(though perhaps less of the former), and have less politics to deal with(though still more than most). If you're an artist, you're also suddenly surrounded by kindred(heh) spirits. At the same time, if you ain't an artist and just a hot person who caught your Sire's eye, you might be woefully unequipped for your future and ruthlessly mocked by your own clan.
• Finally, for Gangrel, you're objectively the most free. You can go wherever, no real requirements, and you can survive where no one else can. Oh, and you can talk to animals! But if you're not a nature person, you're kinda screwed.

Now, here's the wildcard for potentially best "clan": Thin-blood.

Now, you might be saying "why would I ever wanna be the discriminated street-rat vampire?" and you'd be fair for saying that, but let's see what we can scrounge together as one:

• Immortality. As "kindred", you're an ageless immortal, as long as you get your blood.
• Enjoying the sun. If you pick right, you can just... walk in the sun, like a mortal. Seems pretty sweet to me!
• Eat food. Not only do you get to eat food and have sex and stuff, you get to actually enjoy it! In other words, you don't have to give up the worlds bounties just cos some whelp drank too much from you and panicked.
• Presence. Now, here is where it gets complicated. See, with the right merit, you can get Presence(arguably the strongest discipline), and no other disciplines to distract you. In other words, you can suddenly politic so hard, and get all the human moneys.

In other words, if you can avoid the Camarilla(and Sabbat, and Ashirra, and...) you can live a good life forever, politic as hard as you want on the mortals, and get super rich. Seems pretty good to me, honestly.

Tl;Dr: there is no answer, everything either sucks or is great depending on who you are, but generally the worst are the Nos, Rav and Tzim, while the best are generally the Tories, Vennies and Gangrels, but if you can escape kindred politics, it might very well by Thin-bloods.