Unsealed hubs may feel like they spin better, but that's only because of the seals dragging. And there's a world of difference beween spinning an axle in your fingers and how they roll when they're loaded.
Not all sealed hubs are great, flip flop hubs with 14mm axles can be pretty **** because the bearings have to be so small, but if you get a hub with decent sized bearings, Gsports for example, they roll better than pretty much any looseball hub.
As well as sealed bearing hubs requiring very little maintenance the other advantage is none of the components are compromised by having to perform 2 jobs. A cone nut has to be a bearing surface and a nut, 2 functions that require different metallurgical qualities, on a seaed hub the bearing is just a bearing and the cone nut is just a nut.
You might not think it important but when Skyway used to use Campy hubs they had to soften the come nuts quite a bit so that they wouldn't explode when used for freestyle.
For BMX sealed is the way to go
I dunno what the big deal about Povery stuff is, surely it's just generic taiwanese stuff, no better no worse than than most.
And Alex triple walls suck, way too heavy and difficult to true, get a Big City if you want strong rims.