Please note: In the video, I said that backpacks are already moulded on Perry boxes - I meant the little canteens and small sacks and whatsoever, not the big backpacks, which you can glue (or not, if you don't want to). Sorry about that.
This video is meant as a comparison of those two boxes. Conclusion: Warlord Games are more heroic in scale and more bulky, whereas Perry are more realistic. Height is pretty much the same, bulk warries significantly, but they still can be fielded in one army.
Ease of building: Warlord games go together super smoothly, Perry are bit more fiddly.
Parts: In Warlord box, you will have lot of spare parts and can equip your dudes with more SMGs and stuff. In Perry box, you will have much less extra bits. But more soldiers overall.
Details: Both good
Conclusion: Both boxes are great. Perry are cheaper per mini, Warlord games you get bit more variability in how to build them. For exact content of the boxes please watch heaps of other videos that tell about what is in them.