>>42448521
As a Care Package fan I thought about this for a second and the highest killcount is likely Glimmer and Mary.
Glimmer tells Mary "I killed 7 stallions this week" to which Mary answers "you're slacking" which implies that the killcount is higher, but I imagine something like 12, maybe 15 kills in a week.
That's a lot of kills! No wonder the stallion population is dwindling!

Care Package and Apple split killed roughly 30 ponies in 1 hour.
While this doesn't mean that they are always killing ponies with such frequency, in the last episode it was made clear that even out on his day job Care Package was killing. During the Unicorn Heart killing spree Care Package was also doing the majority of the murdering even if it was a team effort.
That is to say that when he isn't being held back by the Equestrian healthcare system, and lets say he get in about 30 kills in a day (which is kind of lowballing it).
That in the space of time Glimmer and Mary have gotten 30 kills in, Care Package alone has likely killed 210 ponies. For funzies.