I have only used drumagog V4 briefly at a friends place. I have had trigger since black friday.
Pros of trigger: The leakage suppression is just tits. The midi it shoots out is very accurate. The samples slate gives out with even EX are pretty nice. You can stack up to 6 different samples per instance of trigger. Trigger instrument editor is easy to use.
Cons of Trigger: People have reported issues triggering trigger using midi instead of audio (sample hit exactly a certain ms after the midi triggers the sample to be played from trigger) in pro tools, not sure about other DAWS. It uses ilok (I see it as a pro mostly but if you don't have an ilok it adds cost on top of the cost of the plugin.
Pros of drumagog: Yeah I don't remember, it triggered well though so lets just say it works haha. Version 4 didn't use an ilok IIRC.
Cons of drumagog: The biggest thing I think I would miss is leakage suppression. I think I could live without slate's samples personally (even though they do sound good, I already have slate plat 3.5).
I would personally go trigger over drumagog.