I broke an X3 recently too (about 5 months old) when sheeting in after a jybe

. Wasn't even that windy. Clearly a material fault. Warranty policy of my local shop in Melbourne was great though, I immediatly got my money back. My first two X3 lasted a lot longer though (2 and 2.5 years, which I though is a decent lifetime for an alloy boom). My weight is only 80kg though.
Cause I was annoyed with the latest breakage I did a bit of research in the Internet and talking to people. All theory as I haven't actually tested lots booms. But it's difficult to try lots of them over longer time periods unless you buy them first

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As far as alloy is concerned I think the Technolimits King (full Ergal) is the best available alloy boom, but you pay for it (roughly as expensive as a hybrid boom). Other good alloy booms seem to be Technolimits (normal alloy), Chinook, Hydrodynamix and Aeron (in no particular order). However, usually the stronger alloy booms are either more expensive, are heavier, have a larger diameter or less extension (or a combination of the previous).
However, a number of people convinced me that alloy booms simply don't last very long if you sail in waves, do hooked in jumps etc. (even if they don't break they may bend) and in the long run may well cost more than a full carbon boom. Also I have small hands and therefore really like the smaller diameters. So I decided to go full carbon. Very expensive at first (I don't trust the cheap no-name ones) but it should last much longer (hopefully).
As far as stiffness is concerned I don't have much experience but I have used both a full carbon boom and a hybrid boom (alloy front, carbon back). The full carbon really made a big difference! The rig feels much better (more direct and doesn't flex as much) especially when it's gusty and pumping works better! The hybrid didn't feel much stiffer than an alloy boom (halfway extended). The weight difference (if there was one) didn't make much difference either, but a smaller diameters (<30mm) feel much better IMHO. I also think both the full carbon and hybrid boom have a lower swing weight (probably lighter extension piece).
That's my 0.02 cents. I'm not affiliated in any way with any of the brands mentioned nor the shops that sell them.