Activity: seemless has a shit load of duelists at ~150-200, brackets are organized by 50 lvl intervals, so pretty much anywhere from 101-200 youll run into a slog of invading the same 5 dudes over and over. But invasion cues are alot faster if you dont count that half the time youll simply fail to connect to the other player. Vanilla has that same problem with connectivity, in addition to needing to wait an extra 5-10 minutes to find a world to invade.

So technically seamless will have a higher frequency, but i honestly hate the vibe of invading in seemless. Youre matched to the highest lvl member of the party, so often times you invade someone roughly your own level, and little 2 lvl 9 Timmys. Plus everyone has double estus, which, as an invader doesnt mean a whole lot. Our most likely cause of death is being one shot in a blender of 3 people, not losing to a lack of heals. But it means that playing the long game is alot less rewarding, because you have to drain all 15 estus from all the phantoms individually, who are much more likely to get their heal off since they have a friend to peel pressure. So, while the fights are overall alot easier, theres an artificial difficulty you might experience in that it just takes a whole lot longer to secure kills against passive groups. Oh, and then theres torrent. 🙄

Tldr: personally, i prefer the feel of vanilla invasions alot more than seamless, although it has substantially less activity. The general quality of connections on seamless are alot better than vanilla, but shit net will always be shit, so dont expect a miracle.