Which is better, getting on oil catch can, vertical pcv mod, or filter in the PCV system? It seems like they all do the same job but the vertical PCV mod is probably the easiest to do?

 

The filter always runs the risk of clogging, or at least presenting an increased resistance and failing to adequately vent the valve covers. Moisture accumulating here can lead to sludging. The vertical PCV mod will limit the oil getting through, but I can't see how the oil will ever make its way back down the PCV pipes into the covers, and there'll always be oil, either as a mist, or under hard cornering, as liquid, getting into the vent pipes.
The catch can is the most effective of the non-intrusive mods, but the valley vent from the LS6 looks like it should be a better fix...though there have been Z06s with oil consumption issues, suspected due to the oil separator not sealing correctly to the underside of the valley plate. Intuitively, I can't see this being as effective at venting the heads, though.