As a prodigious user of combat macros, I wouldn't say no to more lines. Each line is a frame, and as hardware has improved the game's framerate has increased, meaning that (without wait commands) macros take place over shorter windows of time than they once did. More lines means more customization and tuning for macros to make them comfy. Though that said, it's not like macros are in bad shape now, especially since there are plenty of ways to adjust the framerate even for console users.

But if I had to choose between more macro slots and more lines in each macro, I'd definitely choose more macro slots.