I'd suggest you to try both and then decide. I use SP because it was the first portal released for Elkarte, TinyPortal I only install it once on a test forum. The first impression was that it has more options and functionalities compared to SP. Maybe
@tino can explain you better the differences for the two portals.
TinyPortal is in general more detailed in what it can do, although the Elkarte Version is behind the SMF version whilst I sort out some functionality.
SimplePortal is more polished at this current moment in time for Elkarte.
They both largely do the same thing. So try both and decide which one you like more.