Incorrect. Totally different arcs, you guys are trying too hard to make up similarities.
Reason to go:
Alabasta:
Help a friend (temporary crewmate?) save her country from some destruction and a villian ruler.
Skypiea:
FREAKING LOG POSE. And exploring a cool island :D
Plot:
Main Villian:
Crocodile: Logia, Beat Luffy 2 times and almost killed him, had to make Luffy THINK for a second there, looking for the weakspot. A Shichibukai. Used his underlings.
Enel: Logia, Almost lost to Luffy and hardly saved himself by locking Luffy's arm with gold and throwing him off Maxim. Luffy never had to search for a weakspot nor struggle in the ACTUAL FIGHT. Used his underlings. HAD FREAKING MANTRA.
Sidebattles:
Alabasta: Zoro, Nami, Usopp, Chopper, and Sanji all fight.
Skypiea: Nami and Usopp pretty much get ran over than fight, Robin and Chopper "fight".
Sidewarriors:
Alabasta: Rebelions, no real use except maybe Kohza.
Skypiea:Shandians, they fought Zoro (and Luffy?) and got them tired, Wiper almost wiped Enel, Gan Fall fought that priest I can't remember his name…
Charachter development:
Alabasta: Zoro FREAKING CUTS STEEL. Zoro proves he can still improve his skills and is on the way of surpassing Mihawk.
Nami FINALLY fights, and with that awesome Clima Tact. She wins a DF user, who'd believe?
Chopper fights for the first time, together with Usopp, beating two DF users aswell after being screwed over.
Skypiea:
Nothing I can think of, but I bet you'll find. I'm too tired.
Results:
Alabasta: A NEW CREW MEMBER HOLY CRAP. Bounty raise for Luffy, Bounty place for Zoro. Pretty much it, althoug hthe fact they got a new crew member is fucking huge.
Skypiea: 300 mil gold (hich later foudn out as important aswell), Dials, More info on Gol. D Roger/Poneglyphs, More trust in Robin, Going Merry getting in bad condition. An escape from Blackbeard.
*Alabsta had Ace too which is awesome just couldn't compare to anything on Alabasta
Nothing alike. I personally really liked Skypiea much more than Alabasta, but both are good.