Unless you are trying to bring down a bloodthirster, the blade of realities is way too overpriced. O&G have the same weapon (for shamans only though) for half the cost, it uses up most of the oldbloods magic points and is useless against rank and file units. BoRT however is useful against almost everything: ignores heavy armour saves and wounds on a 2+ against T4 foes.
I like the piranah blade, since it does the same thing as my Hive Tyrant does in 40k, and he exels at character hunting. Still a n00b at fantasy, so this is to be taken with a grain of salt...
The piranha blade in my opinion is quite useless. It has no effect on W1 enemies, your oldblood will be having a hard time trying to cause even a single wound against 1+ or 2+ armour save enemies or monsters with T5/6. If you want a good hero hunter, get the oldblood either BoRT or BBoC combined with the maiming shield.
I personally like the BboC more because a) It does very close to the same thing RBoT does (destroy armor) b) it costs alot less and therefore allows for other fun items to be thrown on your Oldblood and c) is flaming which cuts through regeneration and does double wounds to multiple targets. With regen rising in popularity, flaming attacks are becoming very valuable. But out of the poll I chose the Scimitar (+2A). You're now walking around with a character with 7 S5 attacks. That is going to tear through most troops with ease, and even more heavily armored enemies will have trouble just from the sheer number of saves they will have to make.
The Blade of Realities is a near-guaranteed kill against a lot of "problem" units in the uber armies. It also quite quickly becomes the best thing to use against enemies with stacked defenses (high toughness, armor, ward, regen, etc). It also allows you to control the battlefield, as once the enemy knows you have it, he will obsess over it and make his movements more constrained. If you want data to convince you, look at the "Battle of the Oldbloods" series I have started.
And shamans have a whopping 1 attack compared to the 5 thrown out by the old blood, which is why it is dirt cheap. I imagine they also have lower WS. Blade of realities vs heavy cavalry? Or monsters? Or ogres? Even when facing 1W rank and file, you still get 5 attacks at s5, nothing to sneeze at. It is a good weapon. The scimitar, when combined with the maiming shield, can give you great armour and 8 attacks though. Decide whether you want your old blood to hunt big/multi wound creatures, or slaughter infantry. You really need to have a roll in mind for him, and what oyu want him to do in your army.
Blade of Realities is a downright bargain at its current cost. Look at the vampire counts frostblade (or whatever it is called). You actually have to cause a wound to insta-kill something... and it costs 25 points more!
Well I've practically won a dozen times with my O&G thanks to my Savage orc great shaman. He has a boar chariot, 3 attacks with Skull wand of kaloth (same as blade of realities), gets +2 to casting rolls when in close combat and has 4 spells from one of warhammer's greatest magic lores. Come talk to me after you've seen the O&G army book.
Psshht, should have explained that to start with then rather than getting snappy. You said shaman not savage, which do indeed have low WS and only 1 attack. That is a good combo with savage orc shaman. No one would be expecting a shaman to be so aggressive. You don't find that he is a bit fragile and easy to kill? My ASF HEs would enjoy cleaning him up. The ability of the shaman to try to kill the unit champ or even a hero in combat from his magic before attacking would be helpful though.
I'm going with the BBoC for two reasons. 1: There are more things that are vulnerable to flaming attacks (flammable, regen.) then there are units or characters that are immune to them. Coupled with the -2 AS on top of a S5 attack, this is going to cause more damage to more types of units than the rest of them. 2: It's dirt cheap. You can take this weapon and add a talisman and magic armor and an enchanted item on one character, allowing a more survivable old blood on top of the damage dealing capabilities. If you're building to fight a specific army, then this might not necessarily be the weapon of choice for you. But for all around effectiveness, I'm always taking the BBoC.
Yea well he is a T5 with 3 wounds, has 4+ armour and 6+ ward (being a part of the chariot he his hit on a randomised 6 when shooting at him). Not the most toughest character but hey, he is a wizard. You do know that the chariot's S5 impact hits kill your T3, low save elves before they get to "always strike first". Plus he has two boars and orcs to help out, like he wasn't BAD enough.
SoSR... I love this. Especially when mounted on a Carnosaur... Have a look at this topic for why: http://www.lustria-online.com/threads/old-blood-equipment.1059/
Without trying to keep this topic too much off topic, yes I know that impact hits go before ASF but I also know that impact hits do not kill my unit champions or characters, most of which have multiple attacks and at least s5.