I haven't played the Warwick or the Spector. I'd definitely go active pickups, and the 3 band EQ is nice for dialing in your preferred tone on the fly.
The Ibanez has neck through will improve your sustain by a lot, which I love. I love the feel of the Ibanez necks too. They let me play faster than most because they are thinner and I don't have huge hands. It's made of maple, which gives you a bright tone, and average sustain. The neck is Maple/Bubinga, which improves sustain a bit over a pure maple neck.
The Warwick is made of bubinga, so it is going to have tons of sustain, but it will also be a heavier bass...something to consider for stage play. It's going to have about the same tone as the maple bodies though. So more sustain than the Ibanez, about the same tone, depending on the pickups.
The Spector doesn't seem to come in neck through, and has a 3 piece maple neck. I couldn't find out what the body is, only that it is topped with bubinga or maple, so can't say much for tone or sustain. It would be my least favorite choice of the 3 going purely off the build.
You can't go wrong with either the Warwick or the Ibanez. Go play them both back to back and find out which one feels and sounds better to you.
edit - also, after you get your bass, you may want to adjust your truss rod to suit your playing style. http://www.fretnotgu...m/trussrods.htm
has the most comprehensive how to about it. Other things I have read just say to make your neck perfectly straight, which might not be for you (like if you play a lot of slap, or pick hard), and they don't include a lot of the precautions to prevent damage to your instrument.
Believe it or not, a lot of my influence for my bass lines comes from classical music...
This post has been edited by C9H13NO3: 25 October 2007 - 11:04 AM