What are the most and least sound gambits?

Which one is the Albin countergambit again? 

It's not weird at all. Some people consider it a gambit, some don't. You can tell by the name most people do, so, since white wins the pawn back it's a very sound gambit. Not sure why you had to come just to attack people's ratings and 'correct' me.

Crap. He beat me to it. Well, no loss there.

albins is d4, d5, c4, e5

this is the halloween gambit I think

Yep, doesn't get any more unsound than that.

The Halloween gambit is not THAT unsound (it is in fact impossible to refute it beyond =/+).

The Albin should be a draw with best play although it seems rather dubious.  It isn't the foolish pawn drop (I won't even dignify it by calling it a "gambit) that the Englund is and rather tricky, but black has better options. 

The Muzio gambit! I can't believe it is at all sound, sacrificing a whole knight on move 5. 

It was quite popular in the Romantic Era, I believe Morphy played it a few times. 

I thought 4. a3 refuted the Albin?

No you're thinking of the Fajarowicz Budapest.  Actually, maybe 4.a3 refutes the Albin too I'm not familiar with it though. 

The Muzio is definately sound, and Shirov played an even crazier gambit entitled the DOUBLE MUZIO

it goes as followed

1.e4 e5

2.f4 (yes completely sound don't blinking question it) exf5

3.Nf3 g5

4.Bc4 g4

5.0-0(ignoring the treat on the knight. better than moving, and the best move in the position)

5.... gxf3

6. Qxf3 Qf6

7. e5 Qxe5

8. Bxf7 (this is the double muzio, there does exist a triple where b3 is played, but it is undound unlike the double. many great players have played this opening. and the attack is suprisingly strong.)

Muzio is still a strong openning.  If you'd like take a look at this game, we're getting smacked around on the blackside of it

http://www.chess.com/votechess/game?id=51100

I never made a technical evaluation of any gambit's soundness. I got your point; I just didn't agree with it. Some lines are avoided at the top because they are too messy and there is a safer path to advantage. That does not tell us a thing about whether the messy lines are sound. It just tells us that the GM's are trying to avoid a rough day at the office.

The Muzio is completely unsound from an engine point of view, but from a human perspective I think its still playable, although it is extremely rare nowadays at the top level. 

The Muzio is rare because 4. Bc4 is a bad move (instead Nc3 or h4 are best), and because 4. ...g4 is a poor reply to 4. Bc4 (4. ...Bg7 assures black of the advantage).

Bc4 isn't bad it is just a different flavor simple development is almost never bad and on move 4 I could count the bad examples on one hand

that's an interesting idea, I don't know if the albins is totally refuted, but things don't look too good for black after a3.

If you're questioning a gambit's soundness that's a good indication not to play it.  No one questions the Reti, Queen's Gambit, Ruy Lopez, or Giuco Piano's soundness, just saying. 

good point. It works fantastically at blitz though. I remember though I can't find confirmation that one of the top gms played in the rapid knockouts at the fide world cup last year.