MainzMan:I'd rather have an extra 20% when buying credits.
Personally for me, this is the best offer. It then allows you to spend the extra credits on what you want.
By getting a sleeve of balls is nice, but this is simply a way of marketing new balls - ones that players will often never try unless they are given them nor will they the balls again buy again. So from WGT's perspective, simply giving credits away will not promote players to spend more on their future ball purchases.
Also I like David's idea, by giving a ball away with each sleeve, but how would this be done when purchasing the credits? Also I cannot see WGT cutting into this revenue stream quite so easily.
I have always liked the idea of a bulk purchase discount - you are in control of what you are getting, good PR and no messy programming (with no new bugs lol). Yes it is a cost to WGT, but they can then do the sums to see what benefits all parties.