Over the years i have seen some guys say that the hair quality is not that important as systems generally last on average 3 months, so as long as the hair stands up in that time frame it doesn't matter that much, and that good ventilation is the key to a good system?
What in your opinion makes a great hairpiece?
Is it the hair quality or the ventilation techniques, both or something else?

3 months hell what are they doing with them mopping the floor,
My first hair system has lasted me nearly 17 months, granted the lace has gone from the front
Colour change, but still way way better than my r.eceding.hairline

I am not a believer of the 3 month rule. I have hair systems years old that I still could wear. To me what makes a good hair system is pretty simple . This is in no particular order.

1. The materials used - Light, very invisible materials that feel comfortable and look the most invisible. There are a lot of different laces out there, but when you get a really good one it makes a difference

2. how they ventilate it. Having the right hair direction in spots and venting the hairline to look the most natural. I think ventilation makes a huge part of what can make a hair system crappy, good or fantastic.

3. Following instructions.. how it fits your head, making it right to spec, matching the color perfectly bleaching the knots.. giving you the right density t hat you want.

4. Hair quality. Having better hair quality looks and feels better.

5. Getting your order on time without waiting a long time

6. Price point

If any company can satisfy all of these requirements than its a pretty perfect hair system in my opinion.