Steal spell or Force reroll?

[Jlazarin]

I am playing a wizard that is progressing through the Dragon Prophesier prestige class from Magic of Ebberon. My character is a Lvl 5 Wiz / Lvl 8 Dragon. At level 9 I can select between these two extraordinary abilities, but I'm having difficulty determining if one is clearly better than the other:

1. Tiamat: You can attempt to steal a spell as it is being cast by another spellcaster. You must be in prophetic favor and must ready an action to use this ability, though you need not designate a spellcaster target until the ability is activated. The spellcaster must be within 60 feet of you, and you must have line of effect to the caster. You steal the spell with a successful caster level check (DC 10 + the target's caster level). If you are successful, the spell is cast to no effect by the targeted caster, with any material components consumed and any costs to the caster paid as normal. Using this ability immediately ends your prophetic favor. You immediately know which spell you have stolen, and at any time in the next hour, you can activate the stolen spell as a spell-like ability. You use the original caster's caster level, but for all other purposes, you treat the spell as if you had cast it. If you steal a second spell before casting the first, the first spell is lost.

2. Bahamut: Whenever you are in prophetic favor, you can reroll one check or saving throw that you have just made before the DM declares whether the roll results in success or failure. You must take the result of the reroll, even if it is worse than the original roll. Using this ability immediately ends your prophetic favor.

Option 1 is a fun skill, but it's unclear how often I'd use it, since it relies both on guessing when my opponent is going to be casting a particularly powerful spell (wow, I stole a magic missile. cool), and I also then have to overcome a caster level check, which might be difficult against powerful opponents.

Option 2 is a bit more meta-gamey and has less flavor, but would allow me to try to buff a particularly important spell to increase the likelihood it succeeds.

For both of these abilities, my character has to be in a prophetic favor, which usually takes a full round action to re-initialize once it's ended. But as long as I've cast Glimpse of the Prophecy spell (and it hasn't been dispelled) I can re-enter a prophetic favor as immediate action. This would essentially allow me to use Option 2 every turn, and perhaps also use Option 1 each time, but I'd have to sort out the mechanics of when to use the immediate action and ready action, and regardless, I can only hold one stolen spell at a time.

Are there any obvious flaws I'm missing? What would you choose?

[Gauntlet]

Steal Spell looks far more interesting. Can you steal spells from yourself to convert them into SLAs and bypass costs? The caster pays the original cost, but if you cast Gate in portal mode, then steal it from yourself, you should be able to cast it in Calling mode without paying. Same could apply to other spells with a variable cost, like Animate Dead, Fabricate and so on.

Even if that isn't an option, I feel like there are far more sources of rerolls elsewhere than there are sources of fun interesting tricks along these lines, if you want them.

[Jowgen]

For Bahamut's option, first priority in deciding its value is how your DM adjucates its effect in the case of nat 1s. As written you can re-roll them, but a DM might feel that in cases where a Nat 1 is an auto fail, it skips the announcing of success/fail and thus makes it inadmissable. Unlikely the DM would be that punitive, but best to be certain.

For Tiamat's, the main and admittedly rather massive downside of the ability is that it requires you to ready an action. Readies are a pain to adjucate at a table, and in combat you will probably end up with wasted actions as there is no guarantee a given caster will do as you want and cast after you've readied. For comparison, the ring of spell battle from MIC lets you do something similar without requiring a readied action 1/day, although the effect is less flexible (i.e. change target of a spell).

Bahamut's ability also has the massive upside that you can refresh it throughout the day, which puts it leagues above most other re-roll abilities, plus it has both in combat utility (i.e. saves) and out of combat utility by letting you apply it to skill checks.

So in summary, Tiamat's ability gives you a trick you might be able to use to cheese some expensive spells into being cheap with the right set up, and on occasion strategicially hard counter an enemy spellcaster. It's not a consistent ability, but if you can pull it off right it might give you a big return once in a while. Meanwhile, Bahamut's ability is something you'll certainly use almost ever session and you can build on for other optimisations.

In my book, Bahamut wins by a comfortable margin.