Pro's and Con's for each park.  I hope you can form your own opinions from this.

Pros: Kings Dominion

With 15 coasters (counting a possible new hyper) KD would be at least in the top 5 for most coasters in a park. Carowinds would only have 13 and still would be relatively small.  Kings Dominion is a bigger park than Carowinds and a sister park to Kings Island.  It can much easier be converted into a resort- park kind of amusement park.  Cedar Fair probably wants another high-attendance drawling, extremely profitable park and with a hyper coaster that goal becomes more attainable.  The last MAJOR, new coaster Kings Dominion got was Volcano 11 years ago and could see a Canada's Wonderland like spike of attendance with a badly needed, new hyper coaster.  Bottom line, KD needs a new coaster to compete with two heavy hitting parks (Busch Gardens Williamsburg, Six Flags America) for attendance. 

Pros: Carowinds

Carowinds is a smaller park than Kings Dominion and needs a new coaster to compete with the major parks of the world in attendance.  With the log flume removed they have a perfect place to put a new coaster.  The last major new coaster they got was ten years ago, which is not as long as KD has, but is still quite long being coaster starved.  To attract crowds from two big states they need a new coaster and their attendance will skyrocket.  A new coaster would help Carowinds become a major park like Kings Dominion is already.

Cons: Kings Dominion (u don't know how bad it hurts me to do this)

Kings Dominion already has 14 coasters compared to Carowinds' 12.  They just got Dominator in 2008 even though it was relocated.  Even without a coaster they will still be a major park.  Kings Dominion could even get a coaster the year after (2011).  Besides that, Busch Gardens Williamsburg may have a contract with B&M (makes most new hyper coasters and other kinds of coasters) to not make any new coasters for Kings Dominion.  This is a problem considering there are not many other hyper coaster makers and most of them who do make them have not made one for years. 

Cons: Carowinds

Carowinds is the second smallest park (in coasters) from the former Paramount Parks chain.  They considered it a small park not worthy of being treated like a big park.  Carowinds is in a market with no park close to it as far as number if coasters (I think one in Tennessee has 6 and that is the most).  They dominate their market already.  Kings Dominion has to compete on a local scale with parks like Six Flags America and Busch Gardens Williamsburg, they need more coasters because of the high competition to be on top.  KD on a national scale is up there with the big boys like Cedar Point (3 more coasters) and Six Flags Magic Mountain (also 3 more coasters).  Bottom line Cedar Fair needs to give out their coasters to amusement parks who actually need them to compete in their market.