Any really expensive 4 string. If i'm not paying for it i might as well go for something extremely nice.
Thinking WAL, Alembic, Ritter, maybe something with a graphite neck, list could be endless tho.
If it was something i would use on a regular basis and gig with then probably either a Fender J or P or maybe a Sandberg VM4 which is my current gigging bass.
Dave