Here's a study that says that deficit-financed tax cuts are a more effective stimulus method than government spending. I seen other studies which support this as well but don't have a lot of time right now to dig them up.
http://sfb649.wiwi.hu-berlin.de/papers/pdf/SFB649DP2005-039.pdf
Without knowing the specifics of either a tax cut or a spending program one cannot look forward and predict much of anything. Looking backward is valuable IF all the factors are the same as what a program considers and therefore what it expects will occur should have a higher probability than otherwise, but they never are. Some may be similar and you can perhaps give appropriate weight to the those but you've to employ caution when including the dissimilar bits which you, of course, must.
I love it when good economic news pops out which had little or nothing to do with the implemented policy and folks pound their chests claiming credit for that news... no nexus no credit.
I will always favor targeted 'spending' over a tax cut for lots of reasons but one is that tax cuts affect all the tax payers while building a bridge or a dam is far more targeted and quicker. However, a tax cut does have a positive mind set affect while being rather hard to terminate (politically).
Cash for clunkers was generally thought to be a failure but it did have some good results which could have been better if they allowed the cars to be sold to folks. I wonder how many jobs would have been created declunkering those cars using the Bush bucks? Maybe not...
End of the day... The Monetary policy maker actions are almost instantaneous in their affect IF the issue is within their ability to affect. Hopefully they, Treasury and Congress talk to each other.
[EDIT] I should say that a reallocation tax policy from Moonbeam to me, for instance, is not, as I see it a stimulus but it really is if you're a Liberal.