If you are worried about composition then sponge will usually be less pure, it will contain some Cl and maybe other stuff.
Powder is usually a better grade of product.
Sponge isn't really 'sintered'. It's mixed with the alloying elements needed to get to the final desired composition, then pressed into an ingot, and then remelted. P/M titanium products, at least the ones I'm familiar with, are made from prealloyed powder, and are then sintered and hipped, possibly at the same time. Porosity is primarily a function of the sintering and hipping parameters, not so much the powder size and shape, although of course they play a role. And then there's additive manufacturing, using a laser to fuse titanium powder for rapid prototyping. That's yet a different animal.
Can you provide any more context to your question?
I am looking for ru powder which I would like to alloy with an additional metal. The spec I get from my supplier is for ru sponge. I am trying to figure out the outcome of this on the final product.