I think I'd go with Farscape. Both are in my top five, though. But Farscape's worst is probably better than Babylon 5's worst, and its characters come to life more (as they're more of a focus).
Babylon 5's plot definitely outweighs Farscape's, for me, but mileage can and will vary on that as well. B5 goes for a sprawling epic, whereas Farscape keeps things more personal and grounded, but still manages to reach dizzying highs.