We were just having the same exact discussion as OP. We sailed Seaside last year and loved most things about it. Decided to book Meraviglia for a different ship. We’ve read lots of reviews and people seem to love the Meraviglia. We've done both itineraries so that wasn’t a consideration. One thing to note for the OP, the Seaside offers a zipline (which our family loved) and the Meraviglia offers a ropes course. Also, Seaside has an outdoor basketball court versus an indoor court on Meraviglia. Just in case those things matter to you as it does our family. I don’t think you can go wrong