IMHO, I don't think yeast matters as much in a roasty, malty beer like a porter. After brewing nearly 50 batches over the past year, I've gotten to the point where I only use specialty yeast when the recipe really calls for special yeast. Hefe's. Belgians. High Gravs. But for most of my beers, nottingham and Safeale US-05 work just fine. Making a starter and having to order the packs is such a PITA that I just keep a stash of dry yeast around and only order liquid for specialty brews. For a porter, I'd use Nottingham or US-05. But if you really wanna use liquid, the London Ale works well.