Here are your choices :-
Ogre Bulls
...can't have great weapons, they get an Ogre club by default (that's -1 armour save plus the -1 save for a str 4 attack)
You can give your ogre bull an extra hand weapon or an ironfist (this can act as either a shield or an extra weapon - choose before combat begins).
You should definitely upgrade your bulls (you have to take at least one unit of 3+ models) with ironfists and light armour. This will only cost you 8 pts per model. Compare that to upgrading a Bull to a Crusher - a whopping 20 pts for just 1 additional attack ! Don't do it.
Ironguts
...are significantly better fighters than Ogre Bulls, it's all down to their Great Weapons and their higher leadership of 8. You do pay the points for this extra hardness though (an Ogre Bull with an Ogre club is 35 pts, an Irongut with a great weapon and heavy armour. The real question when making your choice is two fold:-1) Will you have the chance to strike first (with your initiative of 2) if you don't take great weapons ?
2) Is your enemy tough or carrying a lot of armour (eg Dwarfs or Bretonnians) ?
3) Will you be facing any enemies with a base size of 40mm ?
If you're facing a high initiative army then taking great weapons will not affect who will strike first because Ogres only have an initiative of 2 anyway.
If you're facing a high toughness opponent (T4 or higher) or an opponent with an armour save of 4 or better then you should take Iron guts because of their great weapons.
Note: if you a facing an enemy with models with the same 40mm base size you can add a very useful magic standard to one of your Irongut units, the:-
Cannibal Totem (25 pts)
- this allows you to reroll missed hits and failed to wound rolls in the first round of combat.Note: don't be tempted to take the...
Bull Standard
...instead of the Cannibal Totem, unless you are fighting an Always Strikes First opponent. (the bull standard is great but it only allows 1 impact hit failed to wound reroll per Ogre in the front rank. The Cannibal Totem allows rerolls for all to hit and to wound for all attacks.
