Right now, Makarov.
I will say that, I do think L's influence would hold better against a mundane threat. Against Kira, people were essentially shadowboxing and being killed at random. A more corporeal threat probably makes L's abilities a lot better, and a lot of those nations inevitably will swing sides. And, it is in Makarov's best interest to find and kill L, whether it is necessary or not, because L is certainly a tangible and unpredictable threat.
Makarov probably wins and probably kills L, but I don't think L is so helpless.