i absolutely agree with the canti hanger thing, meaning if it's there you must use it, i.e no v brakes.
also when both canti bosses and cable hanger and disc mount are all in place on the frame i think it looks better to have an unused disc mount than an unused canti boss/hanger.
with a brand new frame i think you should pick the brake design you want and stick with it. so then the decision is more about the riding to be done on this bike, general XC then v brakes etc will be fine as you know, but for a modern new hardtail i think discs look neater, so i'd go with discs.
edit, if you're building a new but retro-styled bike i'd go for V brake only, this gives an older look but still has the option for reasonably powerful brakes.
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