Warranty work is great if you need it. However, offering a "warranty" to me means nothing if you are down 3 mos waiting or have to tear your crap apart and rebuild it over and over again.
I think most hull builders will stand behind their products to an extent, getting the fix is usually more of a pain than fixing the issue yourself though.
Buikding something strong and worthy of the punishment it will take is the key. Here is what I have seen in the recent past. These are based ONLY on what I see, you asked!
Carbon ROK, broke 2 fairly quickly as they were made using a new to Jeff product and process. I repaired them both and was sent a glass hull kit as payment for my time.
Glass ROK built many and seen many beat on to where any OEM would have been destroyed and these things are INCREDIBLY STRONG
Carbon Freak strong light hulls, few little issues like inserts used are week and the bonline in rear should be stronger but over all a super strong hull so far. Recomend them for sure.
Rickter FS2 and XFS, gorgeous heavy hulls, strong but the finish tends to fail. I do not beleive there is a structural warranty but if it comes in damaged they will make it right.
Q8 incredibly strong and light glass hull period
KDX carbon, Amazing how strong these seem to be for how light they are, definately some high end materials used here and definately the right mix of resin vrs material.
These are the ones I have owned or ridden and been around enough to know. As far as warranty, all I can say is that it will be a HUGE inconveniece to have to use.