Best investment; cartridge or line stage?

Alrighty fellow hifi aficionados, I tried to find a sub on this topic but failed. Here is my bang for the buck question: assuming money spent on either option will be within spitting distance of each other, where am I likely to get more bang for my buck? By investing in a new line stage or investing in a new cartridge. I am currently running a Sutherland TX vibe line stage with a rega aria cartridge on a rega p6 turntable. Appreciate your input! Current system is McIntosh MA252 integrated, rega p6 tt and Martin Logan Vantages.