I've been impressed with the flavours brought out by Belle Saison in the saisons I've been brewing this summer. I know similar flavours wouldn't work in porters and stouts, and wouldn't expect them to even show through because of the strong maltiness and the bitterness of the dark malts, but I'm certainly interested in seeing what distinctive tastes yeasts can bring to the darker beers.
I guess I'm looking for a yeast that is strong and will last the distance, give a fairly clean ferment but perhaps create some interesting stuff that will work with the porter. Peppery and spicy flavours, perhaps.