This is a very good question and difficult to answer. If you ask different brewers this, you will often get a different answer.
The two styles also have different sub-styles that often cross paths. If we look at how, for example, the Vereniging Van Brouwers (Association of Brewers) and the Beer Judge Certification Program in the USA have divided these styles into different sub-styles, we get a better picture.
According to these organizations, a Porter can be divided into three movements: Brown Porter, Robust Porter and Baltic Porter.
They divide a stout into six styles: Dry Stout, Sweet Stout, Oatmeal Stout, Foreign Extra Stout, American Stout and Imperial Stout.
Both beers vary greatly in alcohol percentage. You can find both porters and stouts with alcohol percentages of 5-11 %.
In general, you can deduce that stouts have a drier and more toasty character. Porters, on the other hand, have a slightly more malty and fuller character.
I myself, brew porters with a slightly different malt composition than stouts. A porter gets a little more chocolate malt and a little less of the heavy roasted barley. I also add less hops to porters, so the bitterness is not too intense.
I give the stouts more of the heavier roasted barley and try to accentuate the coffee character more. A stout gets a heavy hopping from me to give a lot of bitterness, which improves the drinkability in my eyes.
Every brewer has his own preference. Some brewers like heavy and quite sweet stouts. I personally like a drier and bitter style better to drink. In short, very personal and nice to discover the style of the brewer.
We have three porters in our range that differ greatly in character:
The Gothic Prince Of Darkness Black Currant Porter: a porter brewed with dark chocolate, vanilla beans and black currants. In this porter, the dark elements of roasted malt, dark chocolate and dark fruit come together very nicely. A truly enjoyable beer, this porter cannot be compared with any other porter.
Raspberry Dipping Chocolate Dripping Super Trouper Porter: A porter brewed with dark chocolate, vanilla beans and raspberries. Slightly heavier in alcohol than the Gothic Prince. Very fresh porter with a special balance between dark chocolate and fresh sour raspberries.
Wake The Hell Up You Can Sleep In The Coffin: A porter brewed with two types of coffee beans from small farmers in Indonesia and Colombia. This coffee has soft, sweet notes. We add lactose (milk sugar) for a wider mouthfeel. We age this beer on Ceylon cinnamon sticks and Madagascar Bourbon Vanilla beans to add smooth flavors and deeper layers to this beer. A real cappuccino in a beer glass!
In addition to these porters, we have two stouts in the selection:
More Complicated Than Your Girlfriend Stout: a nice stout brewed with dark chocolate, coffee and a generous amount of Madagascar Bourbon Vanilla beans. This beer has a nice balance between coffee and chocolate, with an emphasis on the coffee element! The vanilla gives a very creamy and soft touch here.
The Beast Of The East The Bear Is There Russian Imperial Stout: A heavy imperial stout brewed with dark chocolate, cinnamon sticks, vanilla beans, coffee, and roasted chili (Chipotle). This stout emphasizes the chocolate character, has many layers to discover, but remains in balance. The drinkability is amazingly good for such a heavy beer. The Chipotle does not give a hot burning sensation, but a small sting on the tongue, which is a nice surprising experience.
I hope you enjoy discovering our porters and stouts!