"Brush" means different things in different programs. In Photoshop, the Brush tool is anti-aliased, so you don't want to use it for Pixel Art. However, the Pencil tool gives you access to all the same tools as the Brush tool, but retains the aliased edge. In some programs, "Brush" is just the name used for their equivalent of the pencil tool, in some others it means yet other things.
Piskel seems meant more for drawing sprites than tilesets, and I do not see any features for testing tiles or arranging tiles into mockups for testing. I recommend going with another app if you want to do tilesets specifically. I think just about every desktop pixel program has a tile mode these days, though I haven't used them all. I know GrafX2 is a free one that has nice tile support, maybe check that out. Its UI is quite different to Photoshop though, so if you're used to that, you'll have a big learning experience ahead of you.
Photoshop doesn't have tiling tools (automatic updating of all tiles in a mockup, painting with tiles, etc), so it's not that great for doing tilesets. I do my tiles in PS only out of lazy stubbornness xP