It comes down to preference, really. For me, I missed all the stuff that got removed when I played Infinity Skyblock. With no Overworld, most of the fun of the game was missing, which is exploring and finding a visually spectacular place to call home in my opinion.
On the other hand... the guy who runs the server where I played both versions loves Skyblock way more than Regular Infinity... because without the overworld, there's far less load on the server.
That's why I say it boils down to preference. If you run a server you might love Skyblock, but if you're a player who loves to explore, you will much prefer the regular Infinity Evolved modpack. It's nice FTB gave us all such an option with this modpack.
Having played both, I would say there's little to no difference between the two modpacks, from a "technical" standpoint. The gameplay is similar enough that I don't think it would ever be a factor in your choice. I thought the sifting method in Skyblock to get all your raw materials was a bit too simplistic and lacking in complexity. But that goes back to my point about removing the Overworld, and hence, removing all the "good parts" of the game such as mining with a pickaxe!! This is MINEcraft, isn't it?