A number of people who are undoubtedly far more expert than I have discussed strings above; but my experience is kind of counter to the "Spiros for pizz" idea. My fully carved Romanian flatback came with Bel Canto strings - which are supposedly great for arco and underwhelming for pizz. I play (as opposed to practicing) about 99% pizz, in jazz, bluegrass, country, old time, and the like. And I'm still playing the Bel Cantos, with comments like "boy, that bass has a great presence" or "great resonant sound". My concept for upright bass tone is much along the Ray Brown/Walter Page/Charles Mingus line: a big heavy blunt sound, not ringy or twangy at all. For that particular sound, this bass and those (supposedly only good for orchestra) strings work great.
So if you're a pizz player, depending on how you like your bass to sound, it may NOT be that "the one with Spiros will sound better just because of the strings".
So if you're a pizz player, depending on how you like your bass to sound, it may NOT be that "the one with Spiros will sound better just because of the strings".