Seven Nation Army. I don’t care that it’s played on guitar with an octaver. It’s a song where the bass line became a folk song in some parts of the world (meaning the people who sing it don’t associate it with an author because it’s spread by word of mouth). Not the main melody or even the whole song. Just the bass line.
A band I used to play in would jam on it for like 20 minutes. You could literally pull randos from the crowd to sing it and the jam sections could go through just about any genre you wanted. We played it as reggae. We played it as punk. We played it straight. We played it as funk. It’s a really versatile line.
Last thing is that I have to throw in Rush even though they're not necessarily considered as metal as these other ones, but Rush is Rush! I'll go with a more underrated one here. Rush - Circumstances - (Isolated Bass and Drum Track)
If we're doing Sabbath, I have to throw "Electric Funeral" into the ring. The way Geezer plays different variations on the guitar riff really adds to the song.
I can't think of an overall favorite, but here's a few where the bass line is so good I end up focusing on the bass line instead of the main melody, and I'll happily just jam out to the isolated bass stem:
Dean Town - Vulfpeck (ok, it's kind of cheating, but who doesn't wanna listen to Joe Dart play lead bass?)
Innocent Blue - DeviceHigh (admittedly a bit out of left field, but it's got a soft spot in my heart as the first song I ever transcribed and learned on bass)
For some reason my mind is going blank, but if I think of more I'll add them later.
Peter Hook and The Light is great live. Seeing him play both bands worth of material while ripping through those basslines is so fun. Dreams never end always makes me want to dance. Highly recommend if you haven't seen them yet.
Oh wow, that's a complicated question, there's so many right answers depending on personal taste. I like fluorocarbon line. It's more expensive than alternatives, but it's strong stuff, and invisible in water. Why pinch pennies? It can make all the difference between landing the catch and losing it.
Idk what's wrong with me but like... I don't really ever consciously hear the bassline. I took a quiz of famous basslines a while back, and I bombed like all of them even though I knew the songs.
I guess I get why Bass guys are the way they are now.