I've used different strings over the years but lately my string of choice is D'Addario's. [EXL160BT nickel-wound] I used GHS for years before that and still have at least one bass with their Progressives. For flats I've tried a number before settling on LaBella's. I like GHS Precision flats also. As much as strings are a critical element in what a bass sounds like, even using the same brand/type (to my ears) will sound different on different basses. (as in, primarily the pu/electronics as a dominant factor of sound/tone) For me, the consistent 'feel' of the strings bass to bass is what I want once I like the way they sound.
I've strung a bass with new strings right before recording in the past, (as some players do) but lately I don't want to mess with the way they sound and just go with the them regardless of how old they are. I mean, if they sound totally dead I'd change them - but ATC I'm not that picky as long as it sounds good on the other side. Strings don't grow on trees, but it would make for an interesting tree!