Many of us have discussed this at length, including you and I, in the past on IRC.  The biggest reason to switch was in order to discourage pool hoppers from leaving the pool.  After much discussion it was (I thought) decided that pool hopping doesn't actually hurt the pool or the workers in it.  Yes they reduce the payout for all of the shares since there are more of them, but they contribute to more frequent blocks so it all comes out in a wash.  It has been quite a while since I've participated in any discussions, so if the overall consensus has changed, then I digress.

To me determining why is it time to change the payout method affects the preferred method.  If it is "just because" then my vote is to leave it as-is.  "If it ain't broke, don't fix it."  If there is a reason other than an (arguably) irrational fear of pool hopping, choosing a method that best answers to that reason is the way to go.  Is it because the risk is unbalanced between the pool and the workers, then choose the method that shares that risk in the most fair manner.  Is it because there is too much confusion on how proportional payouts work?  Then choose the method that is easier to understand (is there one?)  Is it because proportional is too much load on the servers to calculate payout?  Choose the method with the least load to complete the payout calculations.

In the long run, assuming any fees/charged by the pool are reasonable, it all works out the same for people who have workers that sit and stay in the pool, and payout calculation method really doesn't matter.

Just my 2 bitcents worth.

Jeremy