bitflipper
For example, if you're after a classic pop or Motown sound, it's probably going to be a Fender Precision sample library.
 

Stax too. I just looked at Amblesounds and couldn't see if they mentioned strings. Flatwounds (Labella) being a big part of the Stax Motown sound, you'd want these as part of the set up for any sample sets being made if you are pursuing that sound as much as it being on a P Bass I'd have thought. Interesting that Amplesounds lists its Stingray under it's metal section, not it's bass, but could equally be a Disco Bass.

Thanks so much for all the great inputs ! I really appreciate the wealth of experience that has responded.
 
Certainly, one thing stands out, many of you have acquired multiple bass sample options to cover the range of possibilities. Many of you specifically mention OTS Rick, which I think may well be the largest sample library in size and depth, and I'm certainly leaning towards that one for starters, since I think my flavour of down home Canadian folk pop-rock music style will use that type of sound mostly. (@ bitflipper . . . I've listened to some of your tunes, and think the bass in your recordings is amazing, so sounds like you use that OTS Rick a lot ? . . . though you obviously know a few things about putting it into the mix properly as well)
 
I think I have enough Synth bass sounds to last me a few dozen lifetimes, since I really only use them occasionally for retro type projects. It just takes so long to find the right one because there are too many.
 
I've played Bass guitar in many bands, for a lot of years, so I kind of know the sound I'm looking for, but I never considered myself a good bass player because I always had to cover lead vocals as well, so have spent most of my career thumping out root note bass basics. Now that I'm concentrating more on song composition and recording, a great sounding bass guitar sample will be really helpful, especially if I can get those articulations working easily.
I just haven't been able to determine which of the many bass guitar sample libraries has the best and most flexible articulation package ?
 
Others have mentioned . . ."Alembic, P-Bass", "Ilya Efimov", "Ample Sound's basses", "Stax" . . . I will be sure to search these out, thank you.
 
@ Sidroe . . . you really like "Scarbee Jay-Bass", and I'm wondering if you use it in any basic pop style music. I've  seen a few threads now that people are using this one a lot, but I always though it was for Jazz styles, and Slap bass type stuff. Whenever I try to use a Slap bass sample in my tunes, it just sounds too "uptown" and gets replaced very quickly by something more organic.
 
 

Trilian.

Due for a major upgrade soon...I hope.

My most used seems to be the Scarbee PreBass, usually routed through Amplitube Fender, Ampeg or Orange Bass amp simulations.
 
 
I do like the playability of the Scarbee basses. Apparently Mr Scarbee was a bass player who got arthritis and made the libraries to be as playable as possible.
 
 
The Scarbee Rick is picked and the OT one is fingered. Both are very nice and compliment each other. Both have presets that use Kontakt's built in effects broadening the out of the box appeal. I also like OT Cherry and Jaco a lot. (it would be nice to see the old Jaco get a Evolution style revemp). Cherry was updated a while back and is a good all-rounder with fingered, picked and slap articulations, Its DI so will benefit from being put through an amp sim.
 
 
I only have one Ilya Evtimov bass, the fretless and I like it.
 
 
Finally a couple of off the wall suggestions
 
Ilya Eftimov's Contra Bass Balalaika and Bolder Sounds Guitarron bot make interesting acoustic bass instruments.