As for the historic ones, as mentioned elsewhere on related discussion threads, you can spend a hilarious amount of time at the game start wasting effort to keep historical bloodlines alive- I'll later this week share the new stories of building wonders, but let's just say, it started with me distributing Jewish Concubines to Dyre, Rurik, the Arpads and Harald Fairhair, to make sure they won't die out, and I am right now pondering if I should not just subjugate some tiny county in the west end to have diplomatic range to the British bloodlines before they die out.
Gonna have an easier time though this run- Dyre for once in MY lifetime did not start as demon worshipper, but with the wolf warriors, so there's hopes he wont just bring all his kids to the forest this run!
As for the forged bloodline, this is a trickier question indeed. As mentioned above, you can in theory forge new ones later in the game, and even combine them,but this is a generation-spanning project, and
using a bloodline on your subsequent rulers is also a more than just viable option.
To ease up your decision, I'll simply refer to the complete list of bloodlines on the wiki rather than to give a recommendation- You'll see yourself what would be most useful for your playthrough.
If you want this humble builder's opinion, though, naturally Murder-Builder is the way to go
https://ck2.paradoxwikis.com/Bloodline#Created_Bloodlines
As you'll see however, there are a lot that have significant advantages, so it's really taste and pick.
