My vote is for quality, which does not necessarily mean premium… Shimano for example makes very solid, reliable hubs that build up into a great wheel. If premium means some kind of boutique brand then choose wisely, even then they are not all created equal. Some brands favor light weigh, some engagement, some try to do both…
Personally, I built up my MTB with hope pro-2’s a few years back; I had several reasons. Build quality is top notch, they are user serviceable (as someone else pointed out even well after hope progresses their designs) and they are modular, so i can switch cassette type if I need/want to. (i hold onto my bikes for a long time, so being able to replace/update components is a valuable feature to me) The engagement is frosting on the cake, but not necessary, and I won’t lie, I love the sound. Note though, those last two are not needs, but wants.
Now, some may say the engagement helps when mountain biking… I don’t think it’s necessary, and this is coming from someone who does own and ride a pure trials bike with a high engagement front freewheel and everything. It makes sense when you are trying to pedal kick and a small adjustment of pedal position means cleaning a section or not. However, that kind of riding is not what 99.9% of people do when they go mountain biking, especially if you are talking XCO, XCM or any of the downhill disciplines. I’ve never dabbed on my XC bike because the engagement wasn’t there, others may have different experiences.
My bottom line, aim for quality of build and solid design. I’m not sure if Hope or DT qualify as “premium” if you compare the price tag to I9 or CK, but, they have well executed designs that are simple and reliable. They both spec quality bearings and while not cheap, they won’t break the bank. Again, they both offer pretty quick engagement, but I’m more worried about reliable engagement/function than fast engagement. Personally I’ll avoid ultralight designs, just too many compromises to the design to shave weight in a place where reliability is king (thin flanges, small bearings, poor bearing support, etc…).
Just my $0.02…
one more thought… worth noting that comp style trials bikes these days all run front freewheel designs and the hubs look like track hubs with fixed cogs (threaded and splined designs abound), and a souped up BMX style freewheel mounts to the cranks. The engagement on these freewheels is so tight that if you turn the wheel while the bike is in the work stand, the cranks spin and they do not freewheel, slipping engagement in trials will lead to a crash, so the designs are tuned accordingly. The street trials riders do still use in-hub freewheels, and in that realm hope’s dedicated trials hub dominates the market, with chris king in the running. In those applications both manufacturers opt for a steel free hub body to handle the loads.