Reaver is love, reaver is life.
K now some tips:
Well i suggest go two handed for 2 reasons. First as a reaver your primary abilities are the reaver abilities and secondly even a two handed reaver gets the passives in W&S tree since passives are weapon agnostic. Couple this with bronto sigil and the ability in vanguard which gives you 25% more guard you will now have 100% of you base HP as guard. Vanguard all you need is untouchable defense, charging bull with gore and trample.
The other tree you want is battlemaster with allround great abilities. Horn of valor for guard as nothing beats it, war horn with guard breaker for a 8m aoe which does 100% weapon damage and 1200% vs guard and with chromatic greatsword also does a random elemental damage and helps to provide great CC with fear as well. Finally combat roll is both great evade move and great damage.
The only thing you really need from two handed is shield breaker. Flow of battle is nice but not needed as dragon rage reduces the cooldown of devour on its own.
For weapons go with chromatic greatsword, a brilliant weapon on reaver. IF not then the prismatic greataxe. I find this setup allows me to do quite well in nightmare. Oh and in fallow mire get the on kill stamina amulet as it helps you massively till you land yourself a amulet of death siphon.
Armor you want battlemaster armor with its corresponding arms and legs. Preferred masterworks are critical crafting for weapons, snoufleur skin for 1% hp on hit and bloodstone for 7.5% extra damage for every enemy in 8m radius. I would advice for snoufleur skin and bloodstone/pyrophite with the 7.5% extra damage.
Just remember to get the passives from W&S especially turn the bolt and turn the blade. Since spells fired at you are also affected by these two passives and if possible get bear mauls the wolfs.
Interesting fact to note is a 2 handed reaver has a lot more durability and damage than a two handed templar. Templar instead works best with W&S. While champion is good but horn of valor kinda takes care of all the guard generation need.
Another option is this:
Another note. The battle master tree and horns are if you run them. If you get another warrior to have the horn of valor then you can skip the horns. If you choose this then follow this.
Two Handed tree: 6 points for getting guard breaker and shield breaker ie passives after mighty blow and pommel strike. Keep mighty blow on your skill bar for knocking down shielded guys.
W&S: same as before turn the blade and turn the bolt passives
Vanguard: you want charging bull and livid as well for. Till you get livid go for charging bull via war cry route and use war cry for building guard if needed.
Battlemaster: your final tree to spend points on. The passives are good. Combat roll is ok if you need it. If not then pommel strike will give damage if u need it and livid will get you out status effects.
As before reaver you get everything except the focus ability. Pain bringer toggle for ring of pain, lifeblood for devour and ravage for dragon rage.
Now my preference is for the first build as i find its the most versatile providing good cc, survivability and damage so that is what i generally use. Since Livid the skill might seem awesome just remember that its range is piddly of 5 meters. Fade touched bloodstone with 7.5% extra damage per enemy has 8m and is a passive and therefore better. I personally find livid an annoyance since on bosses its useless as a single mob is only 10% damage and DR while horn of valor gives me 15% damage and 10% guard gen per hit for 10 secs.
Another thing the guard breaker passive after pommel strike is amazing BUT its expensive thing to get as a reaver.