That first one sounds like a real electric bass to me. It's got a lot of slap and slide sounds going on, which are much more work to synthesize than to just play it out on a bass.

If the other ones aren't real basses too, they sound a bit like filtered saw waves. Play around with the cutoff and resonance knobs a bit. Maybe tool around with the filter type.

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Uhm, I'm pretty sure those are real electric basses.
Just try using some samples? Or maybe the Slayer2 VSTi.

I was thinking filtered single saw too, maybe with a subosc (sine?) running for some sub.

The last sample doesn't sound like a real bass guitar to me.

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All rhythm evolves around a kick...

Thanks, I don't think their bass guitar, but I do think it was played through a guitar pedal or some other kind of distortion. Saw with sine subosc sounds likely. I've been playing with V-Station with some external EQ and can get better results with it than my Virus T.I. The V-Station Oscs just have lot more low end, you can go real low on the keys without the low end pussing out.. I'm pretty close, i think some analogue overdrive/distortion is needed to finish it.

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https://soundcloud.com/ghostea stuff

These basslines are also very heavily sidechain-compressed. That's one important factor of the sound of these basses.

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The first bass in that example is sampled from an old Disco Record. The others could be done with Trilogy or even with a synth like Pro-53.