I've raced in the LaSportiva Syborg boots for two seasons now and I'm looking to make that three. Sure, they're a little scuffed up and the one time I lent them out the zipper came back broken, but the liners are still in good shape (minus the stink) and they still skin and ski great!
I've raced in the Dynafit PDG's, Scarpa Alien's, Pierre Gignoux's and in my book the Syborgs still take the cake for a few reasons, number 1 being fit. No matter how light, how well it tours or how well it skis, if your feet hurt the boot isn't going to be that great. Around my ankles I need a lower volume boot, but I have a very wide forefoot. The PDG's were a hair too narrow in the forefoot, which I could've fixed with a punch, but the main problem was that I could never get the boots tight enough to lock my ankles into place. The Scarpa Alien's were wide enough in the forefoot, but still I could get them to ever be snug around my ankles and lower calves (and the Alien's gave me terrible blisters on my heels. I was able to punch out the heel cup which is very narrow, but still couldn't get the upper tight enough).
Right out the box the Syborgs fit perfectly. This is partly from the wrap liner. With the upper and lower velcro on the liner it wraps your feet snugly. A quick side note: when putting these boots on you will want to put the liner on first and then slide into the shell. It's almost impossible to get the liner on comfortably if you put it on while it's in the shell. The lower shell is wide through the forefoot but narrows as it comes back towards the ankle. For those with a little higher volume around the ankles it will require expanding this area to get a comfortable fit. I had to play with the lower buckle to figure out the right tension to keep my feet from moving too much in the shell while not being too tight to make more forefoot uncomfortable. When not in races I will leave this lower pretty looser for the skin up and then crank it tight for the ski down, which helps to prevent over flexing the boot. The upper is also really easy to adjust with a loop of P Chord that can be easily lengthened or shortened and can be set in a number of different positions to best fit your preference.
There are a few other things that have also really impressed me with the Syborg. The Ski/Walk Mode, Warmth and Stiffness have also been better in these boots than in any other race boot I've used. The Ski/Walk mechanism is the same as on Sportiva's $3k all carbon race boot. It is super simple to throw between walk and ski. With the Aliens in order to get them to be tight enough for the ski down it was virtually impossible to throw the rear lever down for ski mode and then even harder to get it back out for walk mode. Same is true for the me for the PDGs.
As for warmth and stiffness, I do not ever remember a day when my feet were cold in these boots and I have definitely been out in them on some very cold days.
Being that these boots are made mostly from Grilamid they are plenty stiff. Obviously it doesn't take much to drive a 700 g race ski, but where I've really been impressed is skiing them with skis like G3 Synapse 92 (1250g) and the Vapor Svelte in a 188 (just over 1000 g). I skied the Synapse 92's on some backcountry missions in the spring and although a beefier boot would have better driven the ski the Syborgs were better suited for a longer tour. With the Sveltes I skied them a full day at the resort with the Syborgs. We were going Chinese Downhill on powder bumps for a solid 4 hours and the only time I even thought about the boots was when I realized I'd been pushing around a 188 cm ski with race boots and not been concerned at all about it not being enough boot.
For the price and weight and fit there is no better race boot for me. The zippered gaiter is a bit delicate and will show wear and tear. This is minor and does not effect performance in anyway and I psyched that I have a race ready to go for it's third straight season.