Funny enough, the seed "river" actually has a pretty long river near spawn, about a whole island length in size. It leads to a bay that then connects to two more rivers. It is also a massive starting island with basically every on it. Honestly wouldn't be awful for speedrunning either, come to think of it.
https://valheim-map.world/?seed=river&offset=-202%2C-22&zoom=0.117&view=0&ver=0.207.20

"liver" is also a good seed. Central lake with three outbound rivers going North, West, and South.
https://valheim-map.world/?seed=liver&offset=-202%2C-22&zoom=0.117&view=0&ver=0.207.20

"worldmap" has a short but thick river
https://valheim-map.world/?seed=worldmap&offset=-577%2C69&zoom=0.076&view=0&ver=0.207.20

"woot" is the opposite. You start on a small island and basically have to set sail in order to get or do anything, which could also be fun. Life on the sea.
https://valheim-map.world/?seed=woot&offset=-139%2C-489&zoom=0.214&view=0&ver=0.207.20

Basically, just put anything you want into valheim-map.world and it will spit out the exact world map.