I will begin by saying all three are vastly overrated, especially the last two. The movies are average at best, and are too slow to develop. Having said that, I enjoyed the first one a lot more than the other two. It had a very gangster feel to it, and the whole Sicilian family thing played out well. The second one was very boring throughout, the plot was very artificial and overly dramatic. I didn't like the whole history lesson on Vito. It made it clear the original story had no substance so they needed filler. The only good part was the ending, not only because it was shockingly surprising, but because it put me out of my misery. The third one was the worse, mainly because the actors weren't as good as in the first two.
Goodfellas is better than all three combined.