Hi all: so I'm wondering why in VN they use the small/red/long pepper but in the US I see most of the time only jalapeno pepper served with pho? Thanks.
This stuff: 
Personally I like the smaller peppers as they are hotter, tastier, have more fragrance, and definitely look better too.
This looks awesome too: 
I think this is more about what's available in particular locality and cost more than anything else. Regardless of what's available/used, presentation matters a lot. For me a better presentation (which helps make the food "taste" better) is when you slice the pepper (any type) thinly rather than thick, as shown in the second photo.
From an operator point of view, in North America, jalapeno peppers are one of the cheapest and most available ever since Viet people started selling pho in the mid-late 1970's. So naturally it was chosen as an acceptable alternative, and it stuck to this day. The lucky thing is, both jalapeno pepper and lime are available in abundance due to the already established Mexican cuisine, plus limes are actually popular and available in VN, so Viet restaurants in NA just use them.
Yep Mexican Jalapeno is not the same as the little red peppers, but you serve what you can get. Like some time restaurants serve lemon instead of lime and it's really not the same goodness. I remember a few years back, lime prices went through the roof, and Vietnamese restaurants, Mexican restaurants, and bars all suffered.
Would agree with @specedpho. Jalapeño peppers were definitely available in abundance and at good prices back in the 1970's. I'm not even sure if other types of peppers were even available except from very specialty vendors, if at all. Remember, garlic in spaghetti used to be considered too "spicy" for American taste not too long ago.
Ooo I love these dangerous red hot little peppers. Vietnamese don't call them "ớt hiểm" (dangerous pepper) for nothing. I have a few of these planted in my backyard and keep the abundant harvest frozen until needed; lasts a long time and still good as just picked.
I'm not a fan of jalapeno peppers for pho. For one thing not all jalapeno peppers are hot all the time; I've had several occasions when it was actually kind of sweet tasting, or not hot at all. The small red peppers are always hot as they should be.
