If you like the idea behind PPLNS but dislike the high share-variance inherent to using a small value of N then perhaps consider trying a pool with using the double-geometric method such as eclipsemc.com or yourbtc.net. Both of these pools have merged mining and 0% fee.
From the eclipsemc.com FAQ: "We are currently employing a modified proportional system with a score based system coming online very shortly." They don't say how that proportional system is modified. And then score-based looks just like Slush.
From the yourbtc.net FAQ: they explain that the value per share decreases progressively over time. That's just like Slush, except that the decay is over a set number of shares instead of a random one. What I like with PPLNS is that shares don't decay, they either count at their full value or don't count at all if we're past N.
Admittedly, I found that yourbtc.net doesn't have as much information on the site about the reward system as I'd have liked. I cannot speak for eclipsemc.com. You can often find more information on the forums. The first page of the main
yourbtc.net thread for example links to much more information. The fact that this thread contains positive posts from respected and knowledgable members of the pool mining community (Inaba and Mein Rosenfeld) is a good sign in my book.
It is true that, when a block is found, more recent shares count for more. You get a smooth descent rather than a clean drop-off. I only suggested it because the parameters of the current implementations of DGM are such that they almost correspond to PPLNS with a relatively large value of N. If the clean drop-off is important to you then DGM is not an option, there are advantages and disadvantages and it largely comes down to a matter of taste. Personally, I prefer the clean drop-off too and have used PPLNS a lot in the past but I fancied a change and, as far as reward systems go, DGM (with non-trivial parameters) is a close second for me. Anyway, it was just a thought. Happy mining!
Note: My choice of reward system and pool is driven primarily by ideology. If the only options were Proportional, SMPPS, and PPS+10%, I'd mine solo. I'd happily pay 5% for PPS or 4% for a good PPLNS/DGM pool.