I prefer lactic for two reasons, apart from taste:
1) Lactic acid is the only acid that will occur naturally in traditional brewhouse processes (you simply can't avoid its presence in beer, and its production is the mechanism of biological acidification in Continental practice) and
2) Phosphoric acid precipitates calcium through apatite reaction, throwing off the balance of your RA and mineral calculations and bringing you back to the beginning, possibly repeatedly.
Both of these points can be overstated, I acknowledge.