Anyone saying Portland or SF has only been to two states in their life or is trolling. I've been all over - grew up in the midwest and have lived on both coasts - the worst towns are in the rust belt. Cleveland is probably at the top (exceeds all expectations of awfulness), but you can't discount Detroit although the small revitalized area is getting nicer. Cincinnati is pretty trash. Richmond VA is not great. Denver is actually pretty ugly on the east side of town. Still like Denver overall though.
That said there would be different answers still if you expanded it to smaller "cities". Fargo ND is very bleak. It would be reasonable to call its biggest attraction a Scheel's department store. Reno is quite depressing, although proximity to Tahoe and Mammoth are the only reason you should find yourself there anyways. Harrisburg PA is also pretty bleak.
On the other side of the coin there are smaller cities that exemplify some of the best of this country. I live in NYC now but probably would only leave domestically if it were to a place like Bend OR, Ann Arbor MI, Mammoth Lakes CA, Ashville NC, etc.