My son is a NICA racer and just managed to outgrown his Small Chisel FS (base Shimano model) in 11 months after a 5" growth spurt. Luckily, we have younger kids so it can be handed down. He's currently about 5'4 1/2". It has been a great bike to him, so I am tempted to just buy a medium Chisel FS since we get a Specialized discount (would get a Comp this round).
However, I am open to other suggestions! There are some great deals on Canyon Lux Trails right now (assuming that a S Lux would serve him for a few years....their sizing is so odd), and we've also considered an Orbea Oiz. Ari Bikes Signal Peak seems promising as well, but I don't think they can give enough of a discount to make that a true contender.
Anything else you think I'm missing? NO HARDTAIL recommendations. We are in a NICA league with more technical trails AND we also ride more technical trails in general.