If talking about from purely shards point of view, skilling at battle field seems to be the fastest, about 1k an hour, but yields VERY little xp. Endurance doesn't need it (soul split is usually enough to keep your health up, the only bosses where you will take damage is pretty much Pest Queen, and there is a way around Nomad's 1 LP attack, which is to Debilitate him, then laugh in his face), Climber on the other hand do, although one could argue that it's the luck of the bosses rather than actual gear setup. Barrows certainly don't need hybrid armor either, the only you'd really need is power armor, since you should, unless you melee or range them with t75 or lower ranged weapons, only take damage from 2 brothers (3 if you count Akrisae), the other 4 shouldn't be able to land more than 1 hit on you (which is why I tend to recommend void armor for barrows, not for its hybrid, but for its damage/accuracy boosts).