Great thread! Here's my input.
Some preliminary information: I weigh 55kg (very light weight) and I surf mainly in Dubai and Abu Dhabi, where wind is quite light and almost never goes over 15 kts.
Primary style of riding: Freeride
Board/Foil setup: Flysurfer/Flydoor4 and Radical4, Airush/Sector V3
Kite Brand: Flysurfer, Airush, Best
Model: Best Waroo 2009, Kahoona V1 and V2, Airush Lithium 2014, Flysurfer Speed 4 Lotus
Sizes: 5.5m (Kahoona V2), 9m (Waroo 2009), 11.5m (Kahoona V1), 14m (Lithium), 18m (Speed 4)
Lowest rideable wind: 7-8 kts on the Speed 4 18m (with extensions)
Highest rideable wind: 30-35kts on the Kahoona 5.5m
What you like about your kites: I hardly use anything else than the Lithium and the Speed 4, as where I am now smaller kites are pretty much useless. So I will concentrate on them, particularly on the Speed 4.
Speed 4 - the good: stable, powerful, light, low bar pressure, great depower and range, strong and quality build. The fabric really repels any dust, sand and water. Water relaunch in normal conditions (8+ kts) is supersimple.
Speed 4 - the bad: not much really. It's sloooow, but what do you expect from a 18m in light wind? Also, I'd like a better rubber quality for the Infinity Bar 2. It is - and it feels - cheap. Hope it got sorted with version 3. Water relaunch in low wind (<8 kts) is a nightmare. But it is for all kites after all.
Lithium - the good: it's a delta, so pulls like a truck. Quality build, fast for its size, reliable and great low end. The Analog Bar that came with it is great - simple, strong, all ropes are plastic-encased. Virtually eternal.
Lithium - the bad: bar pressure is quite high, even at "low" setting, but again, it's a delta. Top end could be better.
What you hate about your kites: No hate at all, just possible improvements highlighted above.
Future plans for your quiver: get rid of the older models (that I don't use anymore anyway), sell the Lithium (I love the kite but it's killing my elbow) and get a full foil quiver, starting with the Speed 4 12m. Also sell the Sector, since I have the flydoor I don't use it anymore.