Both armies are extremely powerful and have a great deal of tactical flexibility.
IMO neither is really more powerful than the other. The war convocation without drop pods has less alpha strike ability but has canticles which give it vastly more tactical flexibility and if played right will put you in a position without any matches that are really bad. At 1500 pts I would try to fit in an ADL so that you can GtG against alpha strike heavy armies and use the fearless canticle to get back up. You can also add a icarus lascannon for a cheap 35 pts extra unit to increase the count for canticles.
Drop pod skitarii does a tremendous amount of damage on the drop. However if you don't have a large number of vanguard it really isn't worth it. Vanguard with their radium guns, -1 cover, BS7, and 3x plasma cavaliers are what make the army work. Those and support from icarus dune crawlers, infiltrators, and dragoons. It is really the synergy of massive threats that the opponent has to deal with turn 1 and the debuffs that make the army work. Without the right combination and synergy you will be an alpha strike and then get annihilated.
I personally prefer the war convocation as it is a more diverse tool box to tackle problems but it is exhausting to run that army well. Drop skitarii is a bit more streamlined but also a more shallow tool box.
BTW if you plan to do drop pods + war convocation make sure you read the canticle rules as the units coming out of DS do NOT count toward determining the level of canticle you get. People are getting that wrong all over the place,,,probably won't matter at 1500 pts but keep it in mind.
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