in Godfather? Godfather Part 2? Part 3?

I would have to say that it is Pacino in parts 1 and 2. The change from college boy to mafia boss and the downfall that follows is amazing.

I'm not really sure about Part 3......maybe Andy Garcia as Vincent. My problem with Pacino in Part 3 was that he was a caricature of himself. In Godfather 1 and 2, Pacino's acting was so subtle, powerful, and perfect. In Godfather 3, he seemed more Big Boy Caprice (his role in Dick Tracy) than Michael Corleone. That's not saying his performance was awful by any means......it just wasn't anywhere near what it was in 1 and 2.

My vote goes to Brando in GF and Michael V. Gazzo in II, nobody in III. But there were so many, many fine performances in GF and II that my choices are just arbitrary.

What about George Hamilton in part 3? haha I kid, I kid. What'd you think of Mantegna as Zasa? I think they should've made Zasa a bigger character

GF I was faultless. I cannot think of a bad performance.

GFII - The guy who played Fanucci hammed it up may have been a bit over the top as was the guy who played the landlord, the latter, however provided good comic relief and perhaps his nervous demeanor was intended to break the tension. Gazzo played the role of a lifetime, and I thought De Niro was brilliant by taking on all of Brando's little ticks and gestures without doing an impersonation. He was a very convincing young Vito.

GFIII is filled with bad and/or lackluster performances, and IMHO FFC's lack of enthusiasm and laziness really showed. I thought the Zasa character was good, but if he had a larger role he would have been overused. IMHO he got whacked at exactly the right time. Of course Hamilton was a disaster, and I have always thought FFC cast him because he got away with the successful casting another horrible actor - Troy Donahue as the hapless Merle. But there are so many miscast parts in III such as Eli Wallach, whoever played Cardinal then pope Lamberto (too saintly), Anthony and a certain family member of the director, and even Andy Garcia who did not convince me that he could trnsform from street thug to smoth mob boss who could trick Altobello and Luchese, just to name a few ....that the carefully crafted charaters of GF I and II become caricatures...even Kate and Mike despite the heroic eforts of Pacino and Keaton to save the movie could not do so. Probably the best acting in III was Talia Shire.

pacino and brando in part 1, pacino and de niro in part 2

GF1- Everybody involved seem to put up a good performance. If I had to pick someone I'd actually go with James Caan. I think he played the "flashy, cocky" character perfectly. He was a great choice to play Santino.

GF2- Al Pacino gets my nod in this movie. In I it was the transition from "college boy" to "don," but at this point he is fully in the "don" stage and he plays the perfect calm, cool and calculated character.

GF3- I kind of like the way Talia Shire did Connie in this movie. It shows her in a different light than the other two films and I think she did a good job showing the transition.

GF-Lucy

GFI - Tough. Very tough. A case can be made for several like Brando, Pacino, Duvall and Caan.

GFII - Of course Pacino once again gave a stellar performance. But for me it's a toss up between Gazzo (Pentangelli), DeNiro (Vito) and Casale (Fredo). I'd have to give the edge to Gazzo (Pentangelli).

GFIII - Talia Shire. At certain moments she over acts just a little bit, a "Bella Mafia" performance at times. But overall I think that Shire does a fantastic job in making her character transform from the meek Connie we are introduced to in GFI, the arrogant and rebelious Connie we see in GFII to the Strong, resilient and somewhat controlling Connie she turns out to be in GFIII. Runner up performance goes to Joe Mantenga. There are times, not many, but times, that Garcia shows a bit of promise in the movie, but like Don T said, overall he's just not convincing.

GF - Duvall and Pacino. Both of them show a large variety of emotions. For example, we see Pacino scared to death in the Restaurant scene. Never again we see such a performance of him again. In GF2 he's playing the "coldhearted bastard" very well who's getting furious twice: "Was it a boy" and when he's slapping Kay. Duvall's performance in GF1 is perfect. You never know whether you should love him or hate him. Best single performance: Duvall's "The Corleones would be outcasts..." Brando and Caan are brilliant too, but we see a narrower spectrum of emotion.
Here I have to admit something: I don't find Diane Keaton convincing.

GF2: Cazale. "I'm smaaht."
I don't think that Gazzo was half as good as Castellano. He must have been drunk all the time.

GF3: Talia Shire.
Here I also have to admit something: I find Sophia Coppolla convincing.

I think all the acting in G1 and GII was superior. It'd be hard to pick just one actor out of so many great performances.

GIII, no one stood out acting wise for me, but that had a lot more to do with the script and even Pacino, Keaton, Garcia, etc. couldn't help.

In the first one, it has to be Brando. He just makes that film larger than life and as iconic as his performance has become, the substance is there. It's simply a pleasure to see him do his thing.

John Cazale is often underrated, and such is the case in Part II. He brings a humanity and a sympathetic side in Fredo's plight, and his performance may even justify Fredo being shunned and lashing out. Fantastic.

As for Part III...I'll say this, Eli Wallach turned in the worst. Ok, maybe Sofia. But Eli wins out because he's a legit actor and that garbling mess of a performance was terrible.

The guy who played Manolo, the landscaper in II.