It depends on how alimony and child support are calculated in your state...which comes first. Quite often child support is first calculated, and then alimony calculated after taking child support into consideration.

However if you are in a state that calculates alimony first, and then child support, then it could make a difference.

Lump sum alimony is also problematic for tax purposes. If you want to be able to be guaranteed that you can deduct the alimony, I wouldn't go the lump sum route. You risk the IRS determining that it was a property settlement rather than alimony.